Biogen (BIIB) 10-Q 21 Jul 16 2016 Q2 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2016	Jul. 15, 2016
Document and Entity Information [Abstract]
Entity Registrant Name	BIOGEN INC.
Entity Central Index Key	875,045
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Document Type	10-Q
Document Period End Date	Jun. 30, 2016
Document Fiscal Year Focus	2,016
Document Fiscal Period Focus	Q2
Amendment Flag	false
Entity Common Stock, Shares Outstanding		219,120,762

Condensed Consolidated Statemen

Condensed Consolidated Statements of Income (Unaudited) - USD ($) shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Revenues:
Product, net	$ 2,466	$ 2,198.6	$ 4,775.4	$ 4,370.9
Revenues from anti-CD20 therapeutic programs	349.2	337.5	678.7	668.1
Other	79	55.6	166.9	107.6
Total revenues	2,894.2	2,591.6	5,621	5,146.6
Cost and expenses:
Cost of sales, excluding amortization of acquired intangible assets	370.3	286.1	683.3	598.6
Research and development	473.1	490.7	910.4	951.3
Selling, general and administrative	492.4	491.9	989.7	1,052.3
Amortization of acquired intangible assets	92.9	92	181.7	187.9
(Gain) loss on fair value remeasurement of contingent consideration	10.6	(2.2)	12.9	5.6
Restructuring charges	0	0	9.7	0
Collaboration profit (loss) sharing	(5.6)	0	(5.6)	0
Total cost and expenses	1,433.7	1,358.5	2,782.1	2,795.6
Income from operations	1,460.5	1,233.1	2,838.9	2,351
Other income (expense), net	(58.5)	(10.9)	(111.3)	(25.9)
Income before income tax expense and equity in loss of investee, net of tax	1,402	1,222.2	2,727.6	2,325.1
Income tax expense	353.6	292.5	710	574.4
Equity in loss of investee, net of tax	0	4.9	0	5.7
Net income	1,048.4	924.8	2,017.6	1,745
Net income (loss) attributable to noncontrolling interests, net of tax	(1.4)	(2.5)	(3.1)	(4.8)
Net income attributable to Biogen Inc.	$ 1,049.8	$ 927.3	$ 2,020.7	$ 1,749.8
Net income per share:
Basic earnings per share attributable to Biogen Inc.	$ 4.79	$ 3.94	$ 9.23	$ 7.44
Diluted earnings per share attributable to Biogen Inc.	$ 4.79	$ 3.93	$ 9.21	$ 7.42
Weighted-average shares used in calculating:
Basic earnings per share attributable to Biogen Inc.	219.1	235.3	219	235.1
Diluted earnings per share attributable to Biogen Inc.	219.4	235.7	219.3	235.7

Condensed Consolidated Stateme3

Condensed Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Statement of Comprehensive Income [Abstract]
Net income attributable to Biogen Inc.	$ 1,049.8	$ 927.3	$ 2,020.7	$ 1,749.8
Other comprehensive income:
Unrealized gains (losses) on securities available for sale, net of tax	4.5	(0.2)	7	1.1
Unrealized gains (losses) on cash flow hedges, net of tax	29.3	(96.2)	(18.3)	(8.9)
Unrealized gains (losses) on pension benefit obligation	0.7	2.9	0.9	4.1
Currency translation adjustment	(58)	63	(48.4)	(37.8)
Total other comprehensive income (loss), net of tax	(23.5)	(30.5)	(58.8)	(41.5)
Comprehensive income attributable to Biogen Inc.	1,026.3	896.8	1,961.9	1,708.3
Comprehensive income (loss) attributable to noncontrolling interests, net of tax	(1.4)	(2.3)	(3.1)	(4.5)
Comprehensive income	$ 1,024.9	$ 894.5	$ 1,958.8	$ 1,703.7

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets (Unaudited) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015
Current assets:
Cash and cash equivalents	$ 1,362	$ 1,308
Marketable securities	2,434.8	2,120.5
Accounts receivable, net	1,293	1,227
Due from anti-CD20 therapeutic programs	334.1	314.5
Inventory	996.4	893.4
Other current assets	1,027.4	836.9
Total current assets	7,447.7	6,700.3
Marketable securities	3,477.6	2,760.4
Property, plant and equipment, net	2,301.8	2,187.6
Intangible assets, net	3,967.6	4,085.1
Goodwill	3,167.1	2,663.8
Investments and other assets	1,153	1,107.6
Total assets	21,514.8	19,504.8
Current liabilities:
Current portion of notes payable and other financing arrangements	4.8	4.8
Taxes payable	212.8	208.7
Accounts payable	225.9	267.4
Accrued expenses and other	2,072.7	2,096.8
Total current liabilities	2,516.2	2,577.7
Notes payable and other financing arrangements	6,538.3	6,521.5
Long-term deferred tax liability	105.6	124.9
Other long-term liabilities	951	905.8
Total liabilities	10,111.1	10,129.9
Commitments and contingencies
Biogen Idec Inc. shareholders' equity
Preferred stock, par value $0.001 per share	0	0
Common stock, par value $0.0005 per share	0.1	0.1
Additional paid-in capital	69.1	0
Accumulated other comprehensive loss	(282.8)	(224)
Retained earnings	14,229.1	12,208.4
Treasury stock, at cost	(2,611.7)	(2,611.7)
Total Biogen Inc. shareholders’ equity	11,403.8	9,372.8
Noncontrolling interests	(0.1)	2.1
Total equity	11,403.7	9,374.9
Total liabilities and equity	$ 21,514.8	$ 19,504.8

Condensed Consolidated Balance5

Condensed Consolidated Balance Sheets (Unaudited) (Parenthetical) - $ / shares	Jun. 30, 2016	Dec. 31, 2015
Statement of Financial Position [Abstract]
Preferred stock, par value	$ 0.001	$ 0.001
Common stock, par value	$ 0.0005	$ 0.0005

Condensed Consolidated Stateme6

Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015
Cash flows from operating activities:
Net income	$ 2,017.6	$ 1,745
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	325.1	292.5
Share-based compensation	84.1	93.7
Deferred income taxes	(30.2)	(90.6)
Other	19.8	(5.8)
Changes in operating assets and liabilities, net:
Accounts receivable	(65)	(38.9)
Inventory	(128.3)	(81.3)
Accrued expenses and other current liabilities	(162.3)	(169.9)
Current taxes payable	(151.7)	102
Other changes in operating assets and liabilities, net	50.1	(66.4)
Net cash flows provided by operating activities	1,959.2	1,780.3
Cash flows from investing activities:
Proceeds from sales and maturities of marketable securities	2,823.6	975.5
Purchases of marketable securities	(3,833.3)	(2,045)
Acquisitions of business, net of cash acquired	0	(198.8)
Purchases of property, plant and equipment	(263.7)	(227.7)
Contingent consideration related to Fumapharm AG acquisition	600	250
Other	(65.9)	(10.1)
Net cash flows used in investing activities	(1,939.3)	(1,756.1)
Cash flows from financing activities:
Purchase of treasury stock	0	(42.2)
Proceeds from issuance of stock for share-based compensation arrangements	(23.9)	(34.7)
Excess tax benefit from share-based awards	9	69.7
Other	1.1	15
Net cash flows provided by financing activities	34	77.2
Net increase in cash and cash equivalents	53.9	101.4
Effect of exchange rate changes on cash and cash equivalents	0.1	(24.2)
Cash and cash equivalents, beginning of the period	1,308	1,204.9
Cash and cash equivalents, end of the period	$ 1,362	$ 1,282.1

Summary of Significant Accounti

Summary of Significant Accounting Policies	6 Months Ended
	Jun. 30, 2016
Accounting Policies [Abstract]
Summary of significant accounting policies	Summary of Significant Accounting Policies Business Overview Biogen is a global biopharmaceutical company focused on discovering, developing, manufacturing and delivering therapies to patients for the treatment of neurological diseases, autoimmune disorders and rare diseases. Our marketed products include TECFIDERA, AVONEX, PLEGRIDY, TYSABRI and FAMPYRA for multiple sclerosis (MS), ELOCTATE for hemophilia A and ALPROLIX for hemophilia B and FUMADERM for the treatment of severe plaque psoriasis. We also have a collaboration agreement with Genentech, Inc. (Genentech), a wholly-owned member of the Roche Group, which entitles us to certain business and financial rights with respect to RITUXAN for the treatment of non-Hodgkin's lymphoma, chronic lymphocytic leukemia (CLL) and other conditions, GAZYVA indicated for the treatment of CLL and follicular lymphoma, and other potential anti-CD20 therapies. In addition to our innovative drug development efforts, we aim to leverage our manufacturing capabilities and scientific expertise through Samsung Bioepis, our joint venture with Samsung BioLogics Co. Ltd. (Samsung Biologics) that develops, manufactures and markets biosimilars as well as through other strategic contract manufacturing partners. Under our commercial agreement with Samsung Bioepis, we market and sell BENEPALI, an etanercept biosimilar referencing ENBREL, and FLIXABI, an infliximab biosimilar referencing REMICADE, in the European Union (E.U.). In May 2016, we announced our intention to spin off our hemophilia business as an independent, publicly traded company. The new company will focus on the discovery and development of therapies for the treatment of hemophilia and other blood disorders, with existing marketed products ELOCTATE and ALPROLIX. The transaction is expected to be completed in early 2017, subject to the satisfaction of certain conditions, including, among others, final approval of our Board of Directors, receipt of a favorable opinion with respect to the tax-free nature of the transaction and the effectiveness of a Form 10 registration statement that will be filed with the Securities and Exchange Commission. The results of our hemophilia business will be included in our condensed consolidated financial statements until the transaction is completed. Basis of Presentation In the opinion of management, the accompanying unaudited condensed consolidated financial statements include all adjustments, consisting of normal recurring accruals, necessary for a fair statement of our financial statements for interim periods in accordance with accounting principles generally accepted in the United States (U.S. GAAP). The information included in this quarterly report on Form 10-Q should be read in conjunction with our consolidated financial statements and the accompanying notes included in our Annual Report on Form 10-K for the year ended December 31, 2015 ( 2015 Form 10-K). Our accounting policies are described in the “ Notes to Consolidated Financial Statements ” in our 2015 Form 10-K and updated, as necessary, in this Form 10-Q. The year-end condensed consolidated balance sheet data presented for comparative purposes was derived from our audited financial statements, but does not include all disclosures required by U.S. GAAP. The results of operations for the three and six months ended June 30, 2016 , are not necessarily indicative of the operating results for the full year or for any other subsequent interim period. We operate as one operating segment, which is discovering, developing, manufacturing and delivering therapies to patients for the treatment of neurological diseases, autoimmune disorders and rare diseases. Consolidation Our condensed consolidated financial statements reflect our financial statements, those of our wholly-owned subsidiaries and those of certain variable interest entities where we are the primary beneficiary. For consolidated entities where we own or are exposed to less than 100% of the economics, we record net income (loss) attributable to noncontrolling interests in our condensed consolidated statements of income equal to the percentage of the economic or ownership interest retained in such entities by the respective noncontrolling parties. Intercompany balances and transactions are eliminated in consolidation. In determining whether we are the primary beneficiary of an entity, we apply a qualitative approach that determines whether we have both (1) the power to direct the economically significant activities of the entity and (2) the obligation to absorb losses of, or the right to receive benefits from, the entity that could potentially be significant to that entity. These considerations impact the way we account for our existing collaborative relationships and other arrangements. We continuously assess whether we are the primary beneficiary of a variable interest entity as changes to existing relationships or future transactions may result in us consolidating or deconsolidating one or more of our collaborators or partners. Use of Estimates The preparation of our condensed consolidated financial statements requires us to make estimates, judgments and assumptions that may affect the reported amounts of assets, liabilities, equity, revenues and expenses and related disclosure of contingent assets and liabilities. On an on-going basis we evaluate our estimates, judgments and methodologies. We base our estimates on historical experience and on various other assumptions that we believe to be reasonable, the results of which form the basis for making judgments about the carrying values of assets, liabilities and equity and the amount of revenues and expenses. Actual results may differ from these estimates under different assumptions or conditions. New Accounting Pronouncements From time to time, new accounting pronouncements are issued by the Financial Accounting Standards Board (FASB) or other standard setting bodies that we adopt as of the specified effective date. Unless otherwise discussed, we do not believe that the impact of recently issued standards that are not yet effective will have a material impact on our financial position or results of operations upon adoption. In May 2014, the FASB issued Accounting Standards Update (ASU) No. 2014-09, Revenue from Contracts with Customers (Topic 606), which supersedes all existing revenue recognition requirements, including most industry-specific guidance. The new standard requires a company to recognize revenue when it transfers goods or services to customers in an amount that reflects the consideration that the company expects to receive for those goods or services. In August 2015, the FASB issued ASU No. 2015-14, Revenue from Contracts with Customers (Topic 606): Deferral of the Effective Date, which delayed the effective date of the new standard from January 1, 2017 to January 1, 2018. The FASB also agreed to allow entities to choose to adopt the standard as of the original effective date. In March 2016, the FASB issued ASU No. 2016-08, Revenue from Contracts with Customers (Topic 606): Principal versus Agent Considerations, which clarifies the implementation guidance on principal versus agent considerations. In April 2016, the FASB issued ASU No. 2016-10, Revenue from Contracts with Customers (Topic 606): Identifying Performance Obligations and Licensing, which clarifies certain aspects of identifying performance obligations and licensing implementation guidance. In May 2016, the FASB issued ASU No. 2016-12, Revenue from Contracts with Customers (Topic 606): Narrow-Scope Improvements and Practical Expedients related to disclosures of remaining performance obligations, as well as other amendments to guidance on collectibility, non-cash consideration and the presentation of sales and other similar taxes collected from customers. These standards have the same effective date and transition date of January 1, 2018. We are currently evaluating the method of adoption and the potential impact that these standards may have on our financial position and results of operations. During 2015, the FASB issued the following new standards, which we adopted on January 1, 2016: • ASU No. 2015-05, Intangibles - Goodwill and Other - Internal-Use Software (Subtopic 350-40): Customer's Accounting for Fees Paid in a Cloud Computing Arrangement. • ASU No. 2015-11, Inventory (Topic 330): Simplifying the Measurement of Inventory. • ASU No. 2015-16, Business Combinations (Topic 805): Simplifying the Accounting for Measurement-Period Adjustments. The adoption of these standards did not have an impact on our financial position or results of operations. For additional information related to these standards, please read Note 1, Summary of Significant Accounting Policies: New Accounting Pronouncements to our consolidated financial statements included in our 2015 Form 10-K. In January 2016, the FASB issued ASU No. 2016-01, Financial Instruments - Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities. The new standard amends certain aspects of accounting and disclosure requirements of financial instruments, including the requirement that equity investments with readily determinable fair values be measured at fair value with changes in fair value recognized in our results of operations. The new standard does not apply to investments accounted for under the equity method of accounting or those that result in consolidation of the investee. Equity investments that do not have readily determinable fair values may be measured at fair value or at cost minus impairment adjusted for changes in observable prices. A financial liability that is measured at fair value in accordance with the fair value option is required to be presented separately in other comprehensive income for the portion of the total change in the fair value resulting from change in the instrument-specific credit risk. In addition, a valuation allowance should be evaluated on deferred tax assets related to available-for-sale debt securities in combination with other deferred tax assets. The new standard will be effective for us on January 1, 2018. The adoption of this standard is not expected to have a material impact on our financial position or results of operations. In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842). The new standard requires that all lessees recognize the assets and liabilities that arise from leases on the balance sheet and disclose qualitative and quantitative information about its leasing arrangements. The new standard will be effective for us on January 1, 2019. The adoption of this standard is not expected to have a material impact on our net financial position, but will impact our assets and liabilities. We are currently evaluating the potential impact that this standard may have on our results of operations. In March 2016, the FASB issued ASU No. 2016-06, Derivatives and Hedging (Topic 815): Contingent Put and Call Options in Debt Instruments. The new standard simplifies the embedded derivative analysis for debt instruments containing contingent call or put options by removing the requirement to assess whether a contingent event is related to interest rates or credit risks. The new standard will be effective for us on January 1, 2017. The adoption of this standard is not expected to have an impact on our financial position or results of operations. In March 2016, the FASB issued ASU No. 2016-07, Investments - Equity Method and Joint Ventures (Topic 323): Simplifying the Transition to the Equity Method of Accounting. The new standard eliminates the requirement that when an investment qualifies for use of the equity method as a result of an increase in the level of ownership interest or degree of influence, an adjustment must be made to the investment, results of operations and retained earnings retroactively on a step-by-step basis as if the equity method had been in effect during all previous periods that the investment had been held. The new standard will be effective for us on January 1, 2017. The adoption of this standard is not expected to have a material impact on our financial position or results of operations. In March 2016, the FASB issued ASU No. 2016-09, Compensation - Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting. The new standard requires recognition of the income tax effects of vested or settled awards in the income statement and involves several other aspects of the accounting for share-based payment transactions, including the income tax consequences, classification of awards as either equity or liabilities and classification on the statement of cash flows. The new standard will be effective for us on January 1, 2017. This standard is not expected to have a material impact on our financial position, results of operations or statements of cash flows upon adoption. In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments. The new standard changes the impairment model for most financial assets and certain other instruments. Under the new standard, entities holding financial assets and net investment in leases that are not accounted for at fair value through net income to be presented at the net amount expected to be collected. An allowance for credit losses will be a valuation account that will be deducted from the amortized cost basis of the financial asset to present the net carrying value at the amount expected to be collected on the financial asset. The new standard will be effective for us on January 1, 2020. The adoption of this standard is not expected to have a material impact on our financial position or results of operations.

Restructuring Restructuring

Restructuring Restructuring	6 Months Ended
	Jun. 30, 2016
Restructuring and Related Activities [Abstract]
Restructuring	Restructuring On October 21, 2015, we announced a corporate restructuring, which included the termination of certain pipeline programs and an 11% reduction in workforce. Under this restructuring, cash payments will total approximately $120 million , of which $15.9 million were related to previously accrued 2015 incentive compensation, resulting in net expected restructuring charges totaling approximately $105 million . These amounts will be substantially paid by the end of 2016. For the three and six months ended June 30, 2016 , we recognized restructuring charges totaling $0.0 million and $9.7 million , respectively. We previously recognized $93.4 million of restructuring charges in our consolidated statements of income during the fourth quarter of 2015. Our restructuring reserve is included in accrued expenses and other in our condensed consolidated balance sheets. The following table summarizes the charges and spending related to our restructuring efforts during the six months ended June 30, 2016 : (In millions) Workforce Reduction Pipeline Programs Total Restructuring reserve as of December 31, 2015 $ 33.7 $ 3.6 $ 37.3 Expense 4.9 5.4 10.3 Payments (28.7 ) (6.0 ) (34.7 ) Adjustments to previous estimates, net (3.5 ) 2.9 (0.6 ) Restructuring reserve as of June 30, 2016 $ 6.4 $ 5.9 $ 12.3

Reserves for Discounts and Allo

Reserves for Discounts and Allowances	6 Months Ended
	Jun. 30, 2016
Sales Discounts, Returns and Allowances, Goods [Abstract]
Reserves for discounts and allowances	Reserves for Discounts and Allowances An analysis of the change in reserves for discounts and allowances is summarized as follows: (In millions) Discounts Contractual Adjustments Returns Total Balance, as of December 31, 2015 $ 56.1 $ 548.7 $ 57.9 $ 662.7 Current provisions relating to sales in current year 266.8 973.8 17.6 1,258.2 Adjustments relating to prior years (2.4 ) 1.6 (5.5 ) (6.3 ) Payments/credits relating to sales in current year (210.2 ) (605.1 ) (0.7 ) (816.0 ) Payments/credits relating to sales in prior years (51.5 ) (384.9 ) (10.4 ) (446.8 ) Balance, as of June 30, 2016 $ 58.8 $ 534.1 $ 58.9 $ 651.8 The total reserves above, included in our condensed consolidated balance sheets, are summarized as follows: (In millions) As of As of Reduction of accounts receivable $ 161.3 $ 144.6 Component of accrued expenses and other 490.5 518.1 Total reserves $ 651.8 $ 662.7

Inventory

Inventory	6 Months Ended
	Jun. 30, 2016
Inventory Disclosure [Abstract]
Inventory	Inventory The components of inventory are summarized as follows: (In millions) As of As of Raw materials $ 235.0 $ 213.0 Work in process 654.6 577.6 Finished goods 139.1 143.0 Total inventory $ 1,028.7 $ 933.6 Balance Sheet Classification: Inventory $ 996.4 $ 893.4 Investments and other assets 32.3 40.2 Total inventory $ 1,028.7 $ 933.6 Inventory included in investments and other assets in our condensed consolidated balance sheets primarily consisted of work in process. As of December 31, 2015 , our inventory included $24.7 million associated with our ZINBRYTA program, $24.2 million associated with the FLIXABI program and $18.4 million associated with the BENEPALI program, which had been capitalized in advance of regulatory approval. The European Commission (EC) approved the marketing authorization applications for BENEPALI and FLIXABI, two anti-tumor necrosis factor (TNF) biosimilars, for marketing in the E.U. in January 2016 and May 2016, respectively, and the U.S. Food and Drug Administration (FDA) approved ZINBRYTA for the treatment of relapsing forms of MS in the U.S. in May 2016.

Intangible Assets and Goodwill

Intangible Assets and Goodwill	6 Months Ended
	Jun. 30, 2016
Goodwill and Intangible Assets Disclosure [Abstract]
Intangible Assets and Goodwill	Intangible Assets and Goodwill Intangible Assets Intangible assets, net of accumulated amortization, impairment charges and adjustments, are summarized as follows: As of June 30, 2016 As of December 31, 2015 (In millions) Estimated Life Cost Accumulated Amortization Net Cost Accumulated Amortization Net Out-licensed patents 13-23 years $ 543.3 $ (514.9 ) $ 28.4 $ 543.3 $ (506.0 ) $ 37.3 Developed technology 15-23 years 3,005.3 (2,604.5 ) 400.8 3,005.3 (2,552.9 ) 452.4 In-process research and development Indefinite until commercialization 692.3 — 692.3 730.5 — 730.5 Trademarks and tradenames Indefinite 64.0 — 64.0 64.0 — 64.0 Acquired and in-licensed rights and patents 6-18 years 3,405.4 (623.3 ) 2,782.1 3,303.2 (502.3 ) 2,800.9 Total intangible assets $ 7,710.3 $ (3,742.7 ) $ 3,967.6 $ 7,646.3 $ (3,561.2 ) $ 4,085.1 For the three and six months ended June 30, 2016 , amortization of acquired intangible assets totaled $92.9 million and $181.7 million , respectively, as compared to $92.0 million and $187.9 million , respectively, in the prior year comparative periods. In-process research and development amounts include adjustments for foreign exchange rate fluctuations. Developed Technology Developed technology primarily relates to our AVONEX product, which was recorded in connection with the merger of Biogen, Inc. and IDEC Pharmaceuticals Corporation in 2003. The net book value of this asset as of June 30, 2016 was $392.8 million . Acquired and In-licensed Rights and Patents Acquired and in-licensed rights and patents primarily relate to our acquisition of all remaining rights to TYSABRI from Elan Corporation plc (Elan). The net book value of this asset as of June 30, 2016 was $2,633.4 million . The increase in acquired and in-licensed rights and patents during the six months ended June 30, 2016 , primarily reflects: • $50.0 million in total milestone payments due to Samsung Bioepis, which became payable upon the approval of BENEPALI and FLIXABI in the E.U. in January 2016 and May 2016, respectively; • $20.0 million milestone payment due to AbbVie Biotherapeutics, Inc. (AbbVie), which became payable upon the regulatory approval of ZINBRYTA in the U.S. in May 2016; and • $26.5 million upon the approval of ALPROLIX in the E.U. in May 2016, which is comprised of a $20.0 million contingent payment due to the former owners of Syntonix Pharmaceuticals, Inc. (Syntonix) and $6.5 million related to the establishment of a corresponding deferred tax liability. For additional information on our relationship with Samsung Bioepis, please read Note 17, Collaborative and Other Relationships to these condensed consolidated financial statements. For additional information on our relationship with Syntonix, please read Note 21, Commitments and Contingencies to our consolidated financial statements included in our 2015 Form 10-K. For additional information on our relationship with AbbVie, please read Note 19, Collaborative and Other Relationships to our consolidated financial statements included in our 2015 Form 10-K. Estimated Future Amortization of Intangible Assets Our amortization expense is based on the economic consumption of intangible assets. Our most significant intangible assets are related to our AVONEX and TYSABRI products. Annually, during our long-range planning cycle, we perform an analysis of anticipated lifetime revenues of AVONEX and TYSABRI. This analysis is also updated whenever events or changes in circumstances would significantly affect the anticipated lifetime revenues of either product. Our most recent long range planning cycle was completed in the third quarter of 2015. Based upon this analysis, the estimated future amortization of acquired intangible assets for the next five years is expected to be as follows: (In millions) As of 2016 (remaining six months) $ 181.6 2017 325.1 2018 298.2 2019 282.7 2020 277.1 2021 265.0 Goodwill The following table provides a roll forward of the changes in our goodwill balance: (In millions) As of Goodwill, beginning of period $ 2,663.8 Increase to goodwill 515.0 Other (11.7 ) Goodwill, end of period $ 3,167.1 The increase in goodwill during the six months ended June 30, 2016 was related to $600.0 million in contingent milestones achieved (exclusive of $85.0 million in tax benefits) and payable to the former shareholders of Fumapharm AG or holders of their rights. Other includes changes in foreign exchange rates. For additional information related to future contingent payments to the former shareholders of Fumapharm AG or holders of their rights, please read Note 19, Commitments and Contingencies to these condensed consolidated financial statements. As of June 30, 2016 , we had no accumulated impairment losses related to goodwill.

Fair Value Measurements

Fair Value Measurements	6 Months Ended
	Jun. 30, 2016
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements The tables below present information about our assets and liabilities that are regularly measured and carried at fair value and indicate the level within the fair value hierarchy of the valuation techniques we utilized to determine such fair value: As of June 30, 2016 (In millions) Total Quoted Prices in Active Markets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Assets: Cash equivalents $ 874.6 $ — $ 874.6 $ — Marketable debt securities: Corporate debt securities 2,290.3 — 2,290.3 — Government securities 2,973.4 — 2,973.4 — Mortgage and other asset backed securities 648.7 — 648.7 — Marketable equity securities 32.4 32.4 — — Derivative contracts 30.1 — 30.1 — Plan assets for deferred compensation 35.6 — 35.6 — Total $ 6,885.1 $ 32.4 $ 6,852.7 $ — Liabilities: Derivative contracts $ 24.8 $ — $ 24.8 $ — Contingent consideration obligations 515.7 — — 515.7 Total $ 540.5 $ — $ 24.8 $ 515.7 As of December 31, 2015 (In millions) Total Quoted Prices in Active Markets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Assets: Cash equivalents $ 909.5 $ — $ 909.5 $ — Marketable debt securities: Corporate debt securities 1,510.9 — 1,510.9 — Government securities 2,875.9 — 2,875.9 — Mortgage and other asset backed securities 494.1 — 494.1 — Marketable equity securities 37.5 37.5 — — Derivative contracts 27.2 — 27.2 — Plan assets for deferred compensation 40.1 — 40.1 — Total $ 5,895.2 $ 37.5 $ 5,857.7 $ — Liabilities: Derivative contracts $ 14.7 $ — $ 14.7 $ — Contingent consideration obligations 506.0 — — 506.0 Total $ 520.7 $ — $ 14.7 $ 506.0 There have been no material impairments of our assets measured and carried at fair value during the three and six months ended June 30, 2016 . In addition, there were no changes in valuation techniques or inputs utilized or transfers between fair value measurement levels during the three and six months ended June 30, 2016 . The fair values of Level 2 instruments classified as cash equivalents and marketable debt securities were determined through third party pricing services. For a description of our validation procedures related to prices provided by third party pricing services, refer to Note 1, Summary of Significant Accounting Policies: Fair Value Measurements , to our consolidated financial statements included in our 2015 Form 10-K. Debt Instruments The fair and carrying values of our debt instruments, which are Level 2 liabilities, are summarized as follows: As of June 30, 2016 As of December 31, 2015 (In millions) Fair Value Carrying Value Fair Value Carrying Value Notes payable to Fumedica $ 6.4 $ 6.1 $ 9.4 $ 9.0 6.875% Senior Notes due March 1, 2018 598.2 561.9 602.6 565.3 2.900% Senior Notes due September 15, 2020 1,561.7 1,507.9 1,497.5 1,485.5 3.625% Senior Notes due September 15, 2022 1,061.0 992.7 1,014.2 992.2 4.050% Senior Notes due September 15, 2025 1,887.3 1,734.1 1,764.6 1,733.4 5.200% Senior Notes due September 15, 2045 1,996.3 1,721.3 1,757.6 1,721.1 Total $ 7,110.9 $ 6,524.0 $ 6,645.9 $ 6,506.5 The fair value of our notes payable to Fumedica was estimated using market observable inputs, including current interest and foreign currency exchange rates. The fair values of each of our series of Senior Notes were determined through market, observable and corroborated sources. For additional information related to our debt instruments, please read Note 11, Indebtedness to our consolidated financial statements included in our 2015 Form 10-K. Contingent Consideration Obligations The following table provides a roll forward of the fair values of our contingent consideration obligations which includes Level 3 measurements: For the Three Months For the Six Months (In millions) 2016 2015 2016 2015 Fair value, beginning of period $ 508.3 $ 461.8 $ 506.0 $ 215.5 Additions — 36.0 — 274.5 Changes in fair value 10.6 (2.2 ) 12.9 5.6 Payments (3.2 ) — (3.2 ) — Fair value, end of period $ 515.7 $ 495.6 $ 515.7 $ 495.6 As of June 30, 2016 and December 31, 2015 , approximately $304.0 million and $301.3 million , respectively, of our contingent consideration obligations valued using Level 3 measurements were reflected as components of other long-term liabilities in our condensed consolidated balance sheets with the remaining balances reflected as a component of accrued expenses and other.

Financial Instruments

Financial Instruments	6 Months Ended
	Jun. 30, 2016
Investments, Debt and Equity Securities [Abstract]
Financial Instruments	Financial Instruments The following table summarizes our financial assets with maturities of less than 90 days from the date of purchase included in cash and cash equivalents on the accompanying condensed consolidated balance sheet: (In millions) As of As of Commercial paper $ 56.9 $ 21.9 Overnight reverse repurchase agreements 66.3 134.7 Money market funds 531.5 673.8 Short-term debt securities 219.9 79.1 Total $ 874.6 $ 909.5 The carrying values of our commercial paper, including accrued interest, overnight reverse repurchase agreements, money market funds and our short-term debt securities approximate fair value due to their short-term maturities. Our overnight reverse repurchase agreements are collateralized with agency-guaranteed mortgage-backed securities and represent approximately 0.3% and 0.7% of total assets as of June 30, 2016 and December 31, 2015 , respectively. The following tables summarize our marketable debt and equity securities, classified as available-for-sale: As of June 30, 2016 (In millions) Fair Value Gross Unrealized Gains Gross Unrealized Losses Amortized Cost Corporate debt securities Current $ 913.4 $ 0.3 $ (0.2 ) $ 913.3 Non-current 1,376.9 7.8 (0.4 ) 1,369.5 Government securities Current 1,521.3 0.6 — 1,520.7 Non-current 1,452.1 3.1 (0.6 ) 1,449.6 Mortgage and other asset backed securities Current 0.1 — — 0.1 Non-current 648.6 1.4 (0.9 ) 648.1 Total marketable debt securities $ 5,912.4 $ 13.2 $ (2.1 ) $ 5,901.3 Marketable equity securities, non-current $ 32.4 $ 0.9 $ (2.1 ) $ 33.6 As of December 31, 2015 (In millions) Fair Value Gross Unrealized Gains Gross Unrealized Losses Amortized Cost Corporate debt securities Current $ 394.3 $ — $ (0.5 ) $ 394.8 Non-current 1,116.6 0.1 (4.1 ) 1,120.6 Government securities Current 1,723.4 0.1 (1.1 ) 1,724.4 Non-current 1,152.5 — (3.1 ) 1,155.6 Mortgage and other asset backed securities Current 2.8 — — 2.8 Non-current 491.3 0.1 (1.8 ) 493.0 Total marketable debt securities $ 4,880.9 $ 0.3 $ (10.6 ) $ 4,891.2 Marketable equity securities, non-current $ 37.5 $ 9.2 $ — $ 28.3 Summary of Contractual Maturities: Available-for-Sale Securities The estimated fair value and amortized cost of our marketable debt securities available-for-sale by contractual maturity are summarized as follows: As of June 30, 2016 As of December 31, 2015 (In millions) Estimated Fair Value Amortized Cost Estimated Fair Value Amortized Cost Due in one year or less $ 2,434.8 $ 2,434.1 $ 2,120.5 $ 2,122.0 Due after one year through five years 3,255.9 3,245.4 2,575.9 2,583.9 Due after five years 221.7 221.8 184.5 185.3 Total available-for-sale securities $ 5,912.4 $ 5,901.3 $ 4,880.9 $ 4,891.2 The average maturity of our marketable debt securities available-for-sale as of June 30, 2016 and December 31, 2015 was approximately 13 months and 16 months , respectively. Proceeds from Marketable Debt Securities The proceeds from maturities and sales of marketable debt securities and resulting realized gains and losses are summarized as follows: For the Three Months For the Six Months (In millions) 2016 2015 2016 2015 Proceeds from maturities and sales $ 1,642.5 $ 601.9 $ 2,823.6 $ 975.5 Realized gains $ 0.6 $ 0.3 $ 1.0 $ 0.5 Realized losses $ (1.2 ) $ (0.5 ) $ (1.6 ) $ (0.8 ) Strategic Investments As of June 30, 2016 and December 31, 2015 , our strategic investment portfolio was comprised of investments totaling $98.3 million and $96.0 million , respectively, which are included in investments and other assets in our condensed consolidated balance sheets. Our strategic investment portfolio includes investments in equity securities of certain biotechnology companies and investments in venture capital funds where the underlying investments are in equity securities of biotechnology companies.

Derivative Instruments

Derivative Instruments	6 Months Ended
	Jun. 30, 2016
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Instruments	Derivative Instruments Foreign Currency Forward Contracts - Hedging Instruments Due to the global nature of our operations, portions of our revenues and operating expenses are recorded in currencies other than the U.S. dollar. The value of revenues and operating expenses measured in U.S. dollars is therefore subject to changes in foreign currency exchange rates. In order to mitigate these changes we use foreign currency forward contracts to lock in exchange rates associated with a portion of our forecasted international revenues and operating expenses. Foreign currency forward contracts in effect as of June 30, 2016 and December 31, 2015 had durations of 1 to 18 months . These contracts have been designated as cash flow hedges and accordingly, to the extent effective, any unrealized gains or losses on these foreign currency forward contracts are reported in accumulated other comprehensive income (loss) (referred to as AOCI in the tables below). Realized gains and losses for the effective portion of such contracts are recognized in revenue when the sale of product in the currency being hedged is recognized and, beginning in the fourth quarter 2015, in operating expenses when the expense in the currency being hedged is recorded. To the extent ineffective, hedge transaction gains and losses are reported in other income (expense), net. The notional value of foreign currency forward contracts that were entered into to hedge forecasted revenues and operating expenses is summarized as follows: Notional Amount Foreign Currency: (In millions) As of As of Euro $ 1,126.5 $ 945.5 Swiss francs 43.5 80.8 Canadian dollar 39.9 76.7 Total foreign currency forward contracts $ 1,209.9 $ 1,103.0 The portion of the fair value of these foreign currency forward contracts that was included in accumulated other comprehensive income (loss) in total equity reflected net losses of $16.4 million and net gains of $1.8 million as of June 30, 2016 and December 31, 2015 , respectively. We expect all contracts to be settled over the next 18 months and any amounts in accumulated other comprehensive income (loss) to be reported as an adjustment to revenue or operating expense. We consider the impact of our and our counterparties’ credit risk on the fair value of the contracts as well as the ability of each party to execute its contractual obligations. As of June 30, 2016 and December 31, 2015 , credit risk did not change the fair value of our foreign currency forward contracts. The following tables summarize the effect of foreign currency forward contracts designated as hedging instruments on our condensed consolidated statements of income: For the Three Months Ended June 30, Net Gains/(Losses) Reclassified from AOCI into Operating Income (Effective Portion) Net Gains/(Losses) Recognized into Net Income (Ineffective Portion) Location 2016 2015 Location 2016 2015 Revenue $ (4.3 ) $ 40.4 Other income (expense) $ 2.1 $ 1.2 Operating expenses $ (0.1 ) $ — Other income (expense) $ — $ — For the Six Months Ended June 30, Net Gains/(Losses) Reclassified from AOCI into Operating Income (Effective Portion) Net Gains/(Losses) Recognized into Net Income (Ineffective Portion) Location 2016 2015 Location 2016 2015 Revenue $ 4.5 $ 75.4 Other income (expense) $ 4.0 $ 3.4 Operating expenses $ (0.2 ) $ — Other income (expense) $ (0.3 ) $ — Interest Rate Contracts - Hedging Instruments We have entered into interest rate swap contracts on certain borrowing transactions to manage our exposure to interest rate changes. In connection with the issuance of our 2.90% Senior Notes, we entered into interest rate swaps with an aggregate notional amount of $675.0 million , which expire on September 15, 2020. The interest rate swap contracts are designated as hedges of the fair value changes in the 2.90% Senior Notes attributable to changes in interest rates. Since the specific terms and notional amount of the swaps match the debt being hedged, it is assumed to be a highly effective hedge and all changes in the fair value of the swaps are recorded as a component of the 2.90% Senior Notes with no net impact recorded in income. Any net interest payments made or received on the interest rate swap contracts are recognized as a component of interest expense in our condensed consolidated statements of income. Foreign Currency Forward Contracts - Other Derivatives We also enter into other foreign currency forward contracts, usually with durations of one month or less, to mitigate the foreign currency risk related to certain balance sheet positions. We have not elected hedge accounting for these transactions. The aggregate notional amount of these outstanding foreign currency contracts was $557.2 million and $721.0 million as of June 30, 2016 and December 31, 2015 , respectively. Net losses of $18.6 million and $16.2 million related to these contracts were recognized as a component of other income (expense), net, for three and six months ended June 30, 2016 , respectively, as compared to net gains of $13.6 million and $3.9 million , respectively, in the prior year comparative periods. Summary of Derivatives While certain of our derivatives are subject to netting arrangements with our counterparties, we do not offset derivative assets and liabilities in our condensed consolidated balance sheets. The following table summarizes the fair value and presentation in our condensed consolidated balance sheets of our outstanding derivatives including those designated as hedging instruments: Fair Value (In millions) Balance Sheet Location As of June 30, 2016 Hedging Instruments: Asset derivatives Other current assets $ 2.0 Investments and other assets $ 23.6 Liability derivatives Accrued expenses and other $ 14.8 Other long-term liabilities $ — Other Derivatives: Asset derivatives Other current assets $ 4.5 Liability derivatives Accrued expenses and other $ 10.0 Fair Value (In millions) Balance Sheet Location As of December 31, 2015 Hedging Instruments: Asset derivatives Other current assets $ 16.6 Investments and other assets $ 0.3 Liability derivatives Accrued expenses and other $ 10.2 Other long-term liabilities $ 2.5 Other Derivatives: Asset derivatives Other current assets $ 10.3 Liability derivatives Accrued expenses and other $ 2.0

Property, Plant and Equipment P

Property, Plant and Equipment Property, Plant and Equipment	6 Months Ended
	Jun. 30, 2016
Property, Plant and Equipment [Abstract]
Property, Plant and Equipment	Property, Plant and Equipment Property, plant and equipment are recorded at historical cost, net of accumulated depreciation. Accumulated depreciation on property, plant and equipment was $1,471.0 million and $1,330.1 million as of June 30, 2016 and December 31, 2015 , respectively. Solothurn, Switzerland Facility On December 1, 2015, we purchased land in Solothurn, Switzerland for 64.4 million Swiss Francs (approximately $62.5 million ). We are building a biologics manufacturing facility on this land in the Commune of Luterbach over the next several years. As of June 30, 2016 and December 31, 2015 , we had approximately $247.8 million and $99.0 million , respectively, capitalized as construction in progress related to the construction of this facility. Cambridge, MA Manufacturing Facility In June 2016, as a result of an evaluation of our manufacturing capabilities and capacity needs based on current and expected future demand, we determined that we intend to cease manufacturing in Cambridge, MA and vacate our 67,000 square foot small-scale biologics manufacturing facility in Cambridge, MA and 46,000 square foot warehouse space in Somerville, MA by the end of 2016. We are currently considering alternatives for the facility, which may include a sale of our rights to the facility and related assets. In the event we are unsuccessful with a sale, we will close the facility by December 31, 2016. As of June 30, 2016 , the carrying value of associated assets totaled approximately $43.0 million and our remaining lease obligation related to these facilities totaled $26.3 million . An impairment assessment as of June 30, 2016 was performed related to the assets, which resulted in no impairments. The anticipated departure from these facilities has shortened the expected useful lives of certain leasehold improvements and other assets at these facilities. As a result, we recorded additional depreciation expense to reflect the assets' new shorter useful lives. As of June 30, 2016 , we recognized approximately $15.8 million of this additional depreciation, which was recorded as cost of sales in our condensed consolidated statements of income.

Equity

Equity	6 Months Ended
	Jun. 30, 2016
Equity [Abstract]
Equity	Equity Total equity as of June 30, 2016 increased $2,028.8 million compared to December 31, 2015 . This increase was primarily driven by net income attributable to Biogen Inc. of $2,020.7 million and an increase in additional paid in capital related to our share-based compensation arrangements, partially offset by other comprehensive losses. Share Repurchases In July 2016, our Board of Directors authorized a program to repurchase up to $5.0 billion of our common stock (2016 Share Repurchase Program). This authorization does not have an expiration date. Repurchased shares will be retired. The 2016 Share Repurchase Program is in addition to the approximately 1.3 million shares remaining under our February 2011 Share Repurchase Program (2011 Share Repurchase Program), which has been used principally to offset common stock issuances under our share-based compensation plans. During the six months ended June 30, 2016 and 2015 , we did not repurchase any shares of common stock under our 2011 Share Repurchase Program. In May 2015, our Board of Directors authorized a program to repurchase up to $5.0 billion of our common stock, which was completed as of December 31, 2015. During the six months ended June 30, 2015 , we repurchased and retired 0.1 million shares of common stock at a cost of $42.2 million . Noncontrolling Interests The following table reconciles equity (deficit) attributable to noncontrolling interests (NCI): For the Three Months For the Six Months (In millions) 2016 2015 2016 2015 NCI, beginning of period $ 1.3 $ 2.7 $ 2.1 $ 5.0 Net income (loss) attributable to NCI, net of tax (1.4 ) (2.5 ) (3.1 ) (4.8 ) Fair value of net assets and liabilities acquired and assigned to NCI — — 0.9 — Translation adjustment and other — 0.2 — 0.2 NCI, end of period $ (0.1 ) $ 0.4 $ (0.1 ) $ 0.4

Accumulated Other Comprehensive

Accumulated Other Comprehensive Income (Loss) Accumulated Other Comprehensive Income (Loss)	6 Months Ended
	Jun. 30, 2016
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Accumulated Other Comprehensive Income (Loss)	Accumulated Other Comprehensive Income (Loss) The following table summarizes the changes in accumulated other comprehensive income (loss), net of tax by component: (In millions) Unrealized Gains (Losses) on Securities Available for Sale Unrealized Gains (Losses) on Cash Flow Hedges Unfunded Status of Postretirement Benefit Plans Translation Adjustments Total Balance, as of December 31, 2015 $ (0.8 ) $ 10.2 $ (37.8 ) $ (195.6 ) $ (224.0 ) Other comprehensive income (loss) before reclassifications 6.6 (13.9 ) 0.9 (48.4 ) (54.8 ) Amounts reclassified from accumulated other comprehensive income (loss) 0.4 (4.4 ) — — (4.0 ) Net current period other comprehensive income (loss) 7.0 (18.3 ) 0.9 (48.4 ) (58.8 ) Balance, as of June 30, 2016 $ 6.2 $ (8.1 ) $ (36.9 ) $ (244.0 ) $ (282.8 ) (In millions) Unrealized Gains (Losses) on Securities Available for Sale Unrealized Gains (Losses) on Cash Flow Hedges Unfunded Status of Postretirement Benefit Plans Translation Adjustments Total Balance, as of December 31, 2014 $ (0.4 ) $ 71.7 $ (31.6 ) $ (99.2 ) $ (59.5 ) Other comprehensive income (loss) before reclassifications 0.9 66.1 4.1 (37.8 ) 33.3 Amounts reclassified from accumulated other comprehensive income (loss) 0.2 (75.0 ) — — (74.8 ) Net current period other comprehensive income (loss) 1.1 (8.9 ) 4.1 (37.8 ) (41.5 ) Balance, as of June 30, 2015 $ 0.7 $ 62.8 $ (27.5 ) $ (137.0 ) $ (101.0 ) The following table summarizes the amounts reclassified from accumulated other comprehensive income: (In millions) Income Statement Location Amounts Reclassified from Accumulated Other Comprehensive Income For the Three Months For the Six Months 2016 2015 2016 2015 Gains (losses) on securities available for sale Other income (expense) $ (0.6 ) $ (0.2 ) $ (0.6 ) $ (0.3 ) Income tax benefit (expense) 0.2 0.1 0.2 0.1 Gains (losses) on cash flow hedges Revenues (4.3 ) 40.4 4.5 75.4 Operating expenses (0.1 ) — (0.2 ) — Other income (expense) — — 0.1 — Income tax benefit (expense) 0.1 (0.2 ) — (0.4 ) Total reclassifications, net of tax $ (4.7 ) $ 40.1 $ 4.0 $ 74.8

Earnings per Share

Earnings per Share	6 Months Ended
	Jun. 30, 2016
Earnings Per Share [Abstract]
Earnings per Share	Earnings per Share Basic and diluted earnings per share are calculated as follows: For the Three Months For the Six Months (In millions) 2016 2015 2016 2015 Numerator: Net income attributable to Biogen Inc. $ 1,049.8 $ 927.3 $ 2,020.7 $ 1,749.8 Denominator: Weighted average number of common shares outstanding 219.1 235.3 219.0 235.1 Effect of dilutive securities: Stock options and employee stock purchase plan 0.1 0.1 0.1 0.1 Time-vested restricted stock units 0.1 0.2 0.1 0.3 Market stock units 0.1 0.1 0.1 0.2 Dilutive potential common shares 0.3 0.4 0.3 0.6 Shares used in calculating diluted earnings per share 219.4 235.7 219.3 235.7 Amounts excluded from the calculation of net income per diluted share because their effects were anti-dilutive were insignificant.

Share-based Payments

Share-based Payments	6 Months Ended
	Jun. 30, 2016
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Share-based Payments	Share-based Payments Share-based Compensation Expense The following table summarizes share-based compensation expense included in our condensed consolidated statements of income: For the Three Months For the Six Months (In millions) 2016 2015 2016 2015 Research and development $ 21.5 $ 22.1 $ 42.9 $ 57.5 Selling, general and administrative 28.7 26.2 63.4 81.8 Restructuring charges — — (1.8 ) — Subtotal 50.2 48.3 104.5 139.3 Capitalized share-based compensation costs (4.4 ) (2.2 ) (7.5 ) (5.6 ) Share-based compensation expense included in total cost and expenses 45.8 46.1 97.0 133.7 Income tax effect (12.7 ) (12.9 ) (27.9 ) (39.6 ) Share-based compensation expense included in net income attributable to Biogen Inc. $ 33.1 $ 33.2 $ 69.1 $ 94.1 The following table summarizes share-based compensation expense associated with each of our share-based compensation programs: For the Three Months For the Six Months (In millions) 2016 2015 2016 2015 Market stock units $ 7.9 $ 9.1 $ 21.3 26.1 Time-vested restricted stock units 33.9 31.8 64.0 63.7 Cash settled performance units 4.6 3.2 4.8 27.0 Performance units 1.3 1.2 8.2 14.4 Employee stock purchase plan 2.5 3.0 6.2 8.1 Subtotal 50.2 48.3 104.5 139.3 Capitalized share-based compensation costs (4.4 ) (2.2 ) (7.5 ) (5.6 ) Share-based compensation expense included in total cost and expenses $ 45.8 $ 46.1 $ 97.0 $ 133.7 We estimate the fair value of our obligations associated with our performance units and cash settled performance units at the end of each reporting period through expected settlement. Cumulative adjustments to these obligations are recorded each quarter to reflect changes in the stock price and estimated outcome of the performance-related conditions. Grants Under Share-based Compensation Plans The following table summarizes our equity grants to employees, officers and directors under our current stock plans: For the Six Months 2016 2015 Market stock units 166,000 179,000 Cash settled performance shares 86,000 115,000 Performance units 56,000 89,000 Time-vested restricted stock units 594,000 375,000 Employee Stock Purchase Plan (ESPP) In June 2015, our stockholders approved the Biogen Inc. 2015 ESPP (2015 ESPP). The 2015 ESPP, which became effective on July 1, 2015, replaced the Biogen Idec Inc. 1995 ESPP (1995 ESPP), which expired on June 30, 2015. The maximum aggregate number of shares of our common stock that may be purchased under the 2015 ESPP is 6,200,000 . For the six months ended June 30, 2016 , approximately 109,000 shares were issued under our 2015 ESPP, compared to approximately 98,000 shares issued under our 1995 ESPP in the prior year comparative period.

Income Taxes

Income Taxes	6 Months Ended
	Jun. 30, 2016
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes A reconciliation between the U.S. federal statutory tax rate and our effective tax rate is summarized as follows: For the Three Months For the Six Months 2016 2015 2016 2015 Statutory rate 35.0 % 35.0 % 35.0 % 35.0 % State taxes 1.0 0.4 1.0 — Taxes on foreign earnings (10.0 ) (11.1 ) (9.0 ) (9.8 ) Credits and net operating loss utilization (1.2 ) (0.7 ) (1.2 ) (0.7 ) Purchased intangible assets 1.1 1.1 1.1 1.0 Manufacturing deduction (1.6 ) (2.1 ) (1.7 ) (1.8 ) Other permanent items 0.6 0.9 0.6 0.7 Other 0.3 0.4 0.2 0.3 Effective tax rate 25.2 % 23.9 % 26.0 % 24.7 % For the three and six months ended June 30, 2016 , compared to the same period in 2015 , our effective tax rate increased primarily due to a state tax benefit in 2015 resulting from the remeasurement of one of our uncertain positions, described below, and a higher relative percentage of our earnings being attributed to the U.S., a higher tax jurisdiction. Accounting for Uncertainty in Income Taxes We and our subsidiaries are routinely examined by various taxing authorities. We file income tax returns in the U.S. federal jurisdiction, various U.S. states and foreign jurisdictions. With few exceptions, including the proposed disallowance we discuss below, we are no longer subject to U.S. federal tax examination for years before 2013 or state, local or non-U.S. income tax examinations for years before 2004. In March 2015, we received a final assessment from the Danish Tax Authority (SKAT) for 2009 regarding withholding taxes and the treatment of certain intercompany transactions involving a Danish affiliate and another of our affiliates. In April 2016, we received final assessments for 2011 and 2013 regarding withholding taxes for similar intercompany transactions. The total amount assessed for 2009, 2011 and 2013 is estimated to be $66.9 million , including interest. For the assessments related to 2011 and 2013, we have made payments to SKAT totaling $13.0 million . We continue to dispute the assessments for all of these periods and believe that the positions we have taken in our historical filings are valid. During the six months ended June 30, 2015, the net effect of adjustments to our uncertain tax positions was a net benefit of approximately $24.0 million primarily related to the state impact of a federal uncertain tax item. It is reasonably possible that we will adjust the value of our uncertain tax positions related to our revenues from anti-CD20 therapeutic programs and certain transfer pricing issues as we receive additional information from various taxing authorities, including reaching settlements with the tax authorities. In addition, the Internal Revenue Service (IRS) and other national tax authorities routinely examine our intercompany transfer pricing with respect to intellectual property related transactions and it is possible that they may disagree with one or more positions we have taken with respect to such valuations. In October 2011, in conjunction with an examination by the IRS, the IRS proposed a disallowance of approximately $130.0 million in deductions for tax years 2007, 2008 and 2009 related to payments for services provided by our wholly owned Danish subsidiary located in Hillerød, Denmark. We initiated a mutual agreement procedure between the IRS and SKAT for the years 2001 through 2009, to reach agreement on the issue. Over the past year, we have reached agreement with the IRS and SKAT regarding the tax treatment of these items for the years up to and including 2009. We have recorded the results of these agreements, which were not significant to our results. In addition, we applied for a bilateral advance pricing agreement for the years 2010 through 2014 to resolve similar issues for those years. In June 2016, we withdrew from the bilateral advance pricing agreement process. We believe that the positions we have taken in our historical filings are valid and supportable and potential changes in these positions are not expected to have a significant impact on our financial position or results of operations.

Other Consolidated Financial St

Other Consolidated Financial Statement Detail	6 Months Ended
	Jun. 30, 2016
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Other Consolidated Financial Statement Detail	Other Consolidated Financial Statement Detail Other Income (Expense), Net Components of other income (expense), net, are summarized as follows: For the Three Months For the Six Months (In millions) 2016 2015 2016 2015 Interest income $ 15.4 $ 4.3 $ 26.6 $ 7.6 Interest expense (65.9 ) (5.8 ) (129.2 ) (12.5 ) Gain (loss) on investments, net (2.7 ) 0.3 (1.1 ) (1.4 ) Foreign exchange gains (losses), net 0.2 (1.5 ) 2.3 (14.5 ) Other, net (5.5 ) (8.2 ) (9.9 ) (5.1 ) Total other income (expense), net $ (58.5 ) $ (10.9 ) $ (111.3 ) $ (25.9 ) Other Current Assets Other current assets includes prepaid taxes totaling approximately $704.1 million and $550.6 million as of June 30, 2016 and December 31, 2015 , respectively. Accrued Expenses and Other Accrued expenses and other consists of the following: (In millions) As of As of Current portion of contingent consideration obligations and milestones $ 556.7 $ 504.7 Revenue-related reserves for discounts and allowances 490.5 518.1 Employee compensation and benefits 228.4 270.8 Royalties and licensing fees 183.7 167.9 Other 613.4 635.3 Total accrued expenses and other $ 2,072.7 $ 2,096.8 Pricing of TYSABRI in Italy - AIFA In the fourth quarter of 2011, Biogen Italia SRL, our Italian subsidiary, received a notice from the Italian National Medicines Agency (Agenzia Italiana del Farmaco or AIFA) that sales of TYSABRI after mid-February 2009 exceeded a reimbursement limit established pursuant to a Price Determination Resolution (Price Resolution) granted by AIFA in December 2006. In January 2012, we filed an appeal in the Regional Administrative Tribunal of Lazio (Il Tribunale Amministrativo Regionale per il Lazio) in Rome, Italy seeking a ruling that the reimbursement limit in the Price Resolution should apply as written to only "the first 24 months" of TYSABRI sales, which ended in mid-February 2009. That appeal is still pending. In June 2014, AIFA approved a resolution affirming that there is no reimbursement limit from and after February 2013. As a result, we recognized $53.5 million of TYSABRI revenues related to the periods beginning February 2013 that were previously deferred. AIFA and Biogen Italia SRL are still discussing a possible resolution for the period from February 2009 through January 2013. We have approximately EUR 75 million recorded as accrued expenses and deferred revenue both included in our long-term liabilities in our condensed consolidated balance sheet for this matter as of June 30, 2016 and December 31, 2015 . For additional information relating to our agreement with AIFA relating to sales of TYSABRI in Italy, please read Note 17, Other Consolidated Financial Statement Detail to our consolidated financial statements included in our 2015 Form 10-K.

Investments in Variable Interes

Investments in Variable Interest Entities	6 Months Ended
	Jun. 30, 2016
Investments in Variable Interest Entities [Abstract]
Investments in Variable Interest Entities	Investments in Variable Interest Entities Consolidated Variable Interest Entities Our condensed consolidated financial statements include the financial results of variable interest entities in which we are the primary beneficiary. Neurimmune SubOne AG In 2007, we entered into a collaboration agreement with Neurimmune SubOne AG (Neurimmune), a subsidiary of Neurimmune AG, for the development and commercialization of antibodies for the treatment of Alzheimer’s disease. Neurimmune conducts research to identify potential therapeutic antibodies and we are responsible for the development, manufacturing and commercialization of all products. Our anti-amyloid beta antibody, aducanumab, for the treatment of Alzheimer’s disease resulted from this collaboration. Based upon our current development plans for aducanumab, we may pay Neurimmune up to $275.0 million in remaining milestone payments. We may also pay royalties in the low-to-mid-teens on sales of any resulting commercial products. We determined that we are the primary beneficiary of Neurimmune because we have the power through the collaboration to direct the activities that most significantly impact the entity’s economic performance and are required to fund 100% of the research and development costs incurred in support of the collaboration agreement. Accordingly, we consolidate the results of Neurimmune. We are required to reimburse Neurimmune for amounts that are incurred by Neurimmune for research and development expenses in support of the collaboration. Amounts reimbursed are reflected in research and development expense in our condensed consolidated statements of income. For the three and six months ended June 30, 2016 and 2015 , these amounts were immaterial. Future milestone payments and royalties, if any, will be reflected in our condensed consolidated statements of income as a charge to noncontrolling interest, net of tax, when such milestones are achieved. The assets and liabilities of Neurimmune are not significant to our financial position or results of operations as it is a research and development organization. We have provided no financing to Neurimmune other than previously contractually required amounts. Other Variable Interest Entities We also consolidate the financial results of our other variable interest entities where we are the primary beneficiary. We may pay these variable interest entities up to approximately $8.0 million in remaining milestone payments. We have provided no financing to these entities other than amounts provided for in the contract. Unconsolidated Variable Interest Entities We have relationships with other variable interest entities that we do not consolidate as we lack the power to direct the activities that significantly impact the economic success of these entities. These relationships include investments in certain biotechnology companies and research collaboration agreements. As of June 30, 2016 and December 31, 2015 , the total carrying value of our investments in biotechnology companies totaled $38.0 million and $29.2 million , respectively. Our maximum exposure to loss related to these variable interest entities is limited to the carrying value of our investments. We have also entered into research collaboration agreements with certain variable interest entities where we are required to fund certain development activities. These development activities are included in research and development expense in our condensed consolidated statements of income, as they are incurred. We have provided no financing to these variable interest entities other than previously contractually required amounts. For additional information related to our investments in variable interest entities, please read Note 18, Investments in Variable Interest Entities to our consolidated financial statements included in our 2015 Form 10-K.

Collaborative and Other Relatio

Collaborative and Other Relationships	6 Months Ended
	Jun. 30, 2016
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Collaborative and Other Relationships	Collaborative and Other Relationships University of Pennsylvania In May 2016, we entered into a collaboration and alliance with the University of Pennsylvania (Penn) to advance gene therapy and gene editing technologies. The collaboration will primarily focus on the development of therapeutic approaches that target the eye, skeletal muscle and the central nervous system. The alliance is also expected to focus on the research and validation of next-generation gene transfer technology using adeno-associated virus gene delivery vectors and exploring the expanded use of genome editing technology as a potential therapeutic platform. During the second quarter of 2016, we paid Penn an upfront amount of $20.0 million , which was recorded as research and development expense in our condensed consolidated statements of income, and prepaid research and development expenditures of $15.0 million , which was recorded in investments and other assets in our condensed consolidated balance sheets. We also expect to fund an additional $47.5 million in the aggregate in research and development costs extending over the next three to five years in seven preclinical research and development programs, as well as the exploration of genome-editing technology. If all of the collaboration programs are successful and we exercise all of our options under the Penn collaboration and alliance, we may be required to make future payments of over $2.0 billion in research funding, options and milestone payments, in addition to royalties payable on net sales of products. Swedish Orphan Biovitrum AB In January 2007, we acquired 100% of the stock of Syntonix. Syntonix had previously entered into a collaboration agreement with Swedish Orphan Biovitrum AB (publ) (Sobi) to jointly develop and commercialize Factor VIII and Factor IX hemophilia products, including ELOCTATE and ALPROLIX. Under an amended and restated collaboration agreement, we have commercial rights for North America (the Biogen North America Territory) and for rest of the world markets outside of the Sobi Territory, as defined below (the Biogen Direct Territory). Following its exercise of an option right, Sobi has assumed commercialization rights for ELOCTA, the trade name for ELOCTATE, and ALPROLIX, in substantially all of Europe, Northern Africa, Russia and certain countries in the Middle East (the Sobi Territory). For additional information on our collaboration agreement with Sobi, please read Note 19, Collaborative and Other Relationships to our consolidated financial statements included in our 2015 Form 10-K. Sobi had its first commercial sale of ELOCTA in January 2016. In March 2016, the EC approved the transfer of the marketing authorization for ELOCTA from Biogen to Sobi, making Sobi the marketing authorization holder of ELOCTA in the E.U. As the marketing authorization holder, Sobi assumes full legal responsibility for ELOCTA, from a regulatory perspective, during its entire life cycle in the E.U. As of June 30, 2016 , approximately $157.0 million in expenditures for ELOCTA, net of an escrow payment and other royalty adjustments as described in the table and its footnote (3) below, are reimbursable to us by Sobi under our collaboration agreement due to Sobi's election to assume final development and commercialization of ELOCTA in the Sobi Territory, which is the Opt-In Consideration for ELOCTA. This reimbursement will be recognized by us as royalty revenue in proportion to collaboration revenues, over a ten year period, consistent with the initial patent term of the product. ALPROLIX was approved in the E.U. by the EC in May 2016 and Sobi had its first commercial sale in June 2016. As of June 30, 2016 , approximately $130.0 million in expenditures for ALPROLIX, net of an escrow payment and other royalty adjustments as described in the table and its footnote (3) below, are reimbursable to us by Sobi under our collaboration agreement due to Sobi's election to assume final development and commercialization of ALPROLIX in the Sobi Territory, which is the Opt-In Consideration for ALPROLIX. This reimbursement will be recognized by us as royalty revenue in proportion to collaboration revenues, over a ten year period, consistent with the initial patent term of the product. We expect to recognize the effect of the cash reimbursement as an adjustment to the Base Rate in the table below over a ten year period, consistent with the initial patent term of the products. Under the collaboration agreement, cash payments are as follows: Rates post Sobi Opt-In (3) Royalty and Net Revenue Share Rates: Method Base Rate following 1st commercial sale in the Sobi Territory: Rate during the Reimbursement Period: Sobi rate to Biogen on net sales in the Sobi Territory Royalty 12% Base Rate Biogen rate to Sobi on net sales in the Biogen North America Territory Royalty 12% Base Rate Biogen rate to Sobi on net sales in the Biogen Direct Territory Royalty 17% Base Rate Biogen rate to Sobi on net revenue (1) from the Biogen Distributor Territory (2) Net 50% Base Rate (1) Net revenue represents Biogen’s pre-tax receipts from third-party distributors, less expenses incurred by Biogen in the conduct of commercialization activities supporting the distributor activities. (2) The Biogen Distributor Territory represents Biogen territories where sales are derived utilizing a third-party distributor. (3) A credit will be issued to Sobi against its reimbursement of the Opt-in Consideration in an amount equal to the difference in the rate paid by Biogen to Sobi on sales in the Biogen territories for certain periods prior to the first commercial sale in the Sobi Territory versus the rate that otherwise would have been payable on such sales. If the reimbursement of the Opt-in Consideration has not been achieved within six years of the first commercial sale of such product, we maintain the right to require Sobi to pay any remaining balances due to us within 90 days of the six year anniversary date of the first commercial sale. Samsung Bioepis Joint Venture Agreement In February 2012, we entered into a joint venture agreement with Samsung BioLogics Co. Ltd. (Samsung Biologics), establishing an entity, Samsung Bioepis, to develop, manufacture and market biosimilar pharmaceuticals. Samsung Biologics contributed 280.5 billion South Korean won (approximately $250.0 million ) for an 85% stake in Samsung Bioepis and we contributed approximately 49.5 billion South Korean won (approximately $45.0 million ) for the remaining 15% ownership interest. Under the joint venture agreement, we have no obligation to provide any additional funding and our ownership interest may be diluted due to financings in which we do not participate. As of June 30, 2016 , our ownership interest is approximately 9% , which reflects the effect of additional equity financings in which we did not participate. We maintain an option to purchase additional stock in Samsung Bioepis that would allow us to increase our ownership percentage up to 49.9% . The exercise of this option is within our control and is based on paying for 49.9% of the total investment made by Samsung Biologics into Samsung Bioepis in excess of what we have already contributed under the agreement plus a rate that will represent their return on capital. Based on our level of influence over Samsung Bioepis, we account for this investment under the equity method of accounting and we recognize our share of the results of operations related to our investment in Samsung Bioepis one quarter in arrears when the results of the entity become available, which is reflected as equity in loss of investee, net of tax in our condensed consolidated statements of income. During the three and six months ended June 30, 2015 , we recognized a loss on our investment of $4.9 million and $5.7 million , respectively. During 2015, as our share of losses exceeded the carrying value of our investment, we suspended recognizing additional losses and will continue to do so unless we commit to providing additional funding. Commercial Agreement In December 2013, pursuant to our rights under the joint venture agreement with Samsung Biologics, we entered into an agreement with Samsung Bioepis to commercialize, over a 10-year term, three anti-TNF biosimilar product candidates in Europe and in the case of one anti-TNF biosimilar, Japan. Under the terms of this agreement, we have made total upfront and milestone payments of $46.0 million , which have been recorded as a research and development expense in our condensed consolidated statements of income as the programs they relate to had not achieved regulatory approval. We also agreed to make an additional milestone payment of $25.0 million upon regulatory approval in the E.U. for each of the three anti-TNF biosimilar product candidates. During the six months ended June 30, 2016 , we made a $25.0 million milestone payment and accrued another $25.0 million , which have been capitalized in intangible assets, net in our condensed consolidated balance sheet as BENEPALI received regulatory approval in the E.U. in January 2016 and FLIXABI received regulatory approval in the E.U. in May 2016. We began to recognize revenue on sales of BENEPALI in the E.U. in the first quarter of 2016. We reflect revenues on sales of BENEPALI to third parties in product revenues, net in our condensed consolidated statements of income and record the related cost of revenues and sales and marketing expenses in our condensed consolidated statements of income to their respective line items when these costs are incurred. We share 50% of the profit or loss related to our commercial agreement with Samsung Bioepis. This profit share with Samsung Bioepis is recognized in collaboration profit (loss) sharing in our condensed consolidated statements of income. Other Services Simultaneous with the formation of Samsung Bioepis, we also entered into a license agreement, a technical development services agreement and a manufacturing agreement with Samsung Bioepis. For the three and six months ended June 30, 2016 , we recognized $14.2 million and $16.9 million , respectively, in relation to these services as other revenues in our condensed consolidated statements of income, as compared to $17.2 million and $36.1 million , respectively, in the prior year comparative periods. For additional information related to our other significant collaboration arrangements, please read Note 19, Collaborative and Other Relationships to our consolidated financial statements included in our 2015 Form 10-K.

Litigation

Litigation	6 Months Ended
	Jun. 30, 2016
Loss Contingency, Information about Litigation Matters [Abstract]
Litigation	Litigation We are currently involved in various claims and legal proceedings, including the matters described below. For information as to our accounting policies relating to claims and legal proceedings, including use of estimates and contingencies, please read Note 1, Summary of Significant Accounting Policies to our consolidated financial statements included in our 2015 Form 10-K. With respect to some loss contingencies, an estimate of the possible loss or range of loss cannot be made until management has further information, including, for example, (i) which claims, if any, will survive dispositive motion practice; (ii) information to be obtained through discovery; (iii) information as to the parties' damages claims and supporting evidence; (iv) the parties’ legal theories; and (v) the parties' settlement positions. The claims and legal proceedings in which we are involved also include challenges to the scope, validity or enforceability of the patents relating to our products, pipeline or processes, and challenges to the scope, validity or enforceability of the patents held by others. These include claims by third parties that we infringe their patents. An adverse outcome in any of these proceedings could result in one or more of the following and have a material impact on our business or consolidated results of operations and financial position: (i) loss of patent protection; (ii) inability to continue to engage in certain activities; and (iii) payment of significant damages, royalties, penalties and/or license fees to third parties. Loss Contingencies Forward Pharma German Patent Litigation On November 18, 2014, Forward Pharma A/S (Forward Pharma) filed suit against us in the Regional Court of Dusseldorf, Germany alleging that TECFIDERA infringes German Utility Model DE 20 2005 022 112 U1 (the utility model), which was issued in April 2014 and expired in October 2015. Forward Pharma subsequently extended its allegations to assert that TECFIDERA infringes Forward Pharma's European Patent No. 2 801 355, which was issued in May 2015 and expires in October 2025 (the '355 patent). Forward Pharma seeks declarations of infringement and damages for our sales of TECFIDERA in Germany. Under German law, disgorgement of profits on infringing sales is a measure of damages. With respect to the '355 patent, the hearing has been stayed pending the outcome of opposition proceedings that we and others have filed in the European Patent Office, and with respect to the utility model the hearing has been stayed pending the outcome of those proceedings and proceedings in the German Patent Office. ALPROLIX Patent Licensing Matter We are in discussions with Pfizer regarding its proposal that we take a license to its U.S. Patent No. 8,603,777 (Expression of Factor VII and IX Activities in Mammalian Cells) and pay royalties on sales of ALPROLIX. An estimate of the possible loss or range of loss cannot be made at this time. Italian National Medicines Agency In the fourth quarter of 2011, Biogen Italia SRL received notice from the Italian National Medicines Agency (Agenzia Italiana del Farmaco or AIFA) that sales of TYSABRI after mid-February 2009 exceeded a reimbursement limit established pursuant to a Price Determination Resolution (Price Resolution) granted by AIFA in December 2006. On January 12, 2012, we filed an appeal in the Regional Administrative Tribunal of Lazio (Il Tribunale Amministrativo Regionale per il Lazio) in Rome, Italy seeking a ruling that the reimbursement limit in the Price Resolution should apply as written to only “the first 24 months” of TYSABRI sales, which ended in mid-February 2009. The appeal is still pending. In June 2014, AIFA approved a resolution affirming that there is no reimbursement limit from and after February 2013. AIFA and Biogen Italia SRL are discussing a possible resolution for the period from February 2009 through January 2013. For additional information regarding this matter, please read Note 15, Other Consolidated Financial Statement Detail to these condensed consolidated financial statements. Qui Tam Litigation On July 6, 2015, four qui tam actions filed against us by relators suing on behalf of the United States and certain states were unsealed by the U.S. District Court for the District of Massachusetts. All but one of the actions has been voluntarily dismissed. The pending action alleges sales and promotional activities in violation of the federal False Claims Act and state law counterparts, and seeks single and treble damages, civil penalties, interest, attorneys’ fees and costs. The complaint was recently amended, and we intend to move to dismiss. The United States has not made an intervention decision. An estimate of the possible loss or range of loss cannot be made at this time. Securities Litigation We and certain current and former officers are defendants in In re Biogen Inc. Securities Litigation, filed by a shareholder on August 18, 2015 in the U.S. District Court for the District of Massachusetts. The amended complaint alleges violations of federal securities laws under 15 U.S.C. §78j(b) and §78t(a) and 17 C.F.R. §240.10b-5. The lead plaintiff sought a declaration of the action as a class action, certification as a representative of the class and its counsel as class counsel, and an award of damages, interest and attorneys' fees. On July 1, 2016 the U.S. District Court dismissed the case. An estimate of the possible loss or range of loss cannot be made at this time. Other Matters Interference Proceeding with Forward Pharma In April 2015, the U.S. Patent and Trademark Office (USPTO) declared an interference between Forward Pharma’s pending U.S. Patent Application No. 11/576,871 and our U.S. Patent No. 8,399,514 (the '514 patent). The '514 patent includes claims covering the treatment of multiple sclerosis with 480 mg of dimethyl fumarate as provided for in our TECFIDERA label. A hearing has been scheduled for late 2016. Inter Partes Review Petitions and Proceeding On March 22, 2016, the USPTO instituted inter partes review of the '514 patent on the petition of the Coalition for Affordable Drugs V LLC, an entity associated with a hedge fund. A hearing has been scheduled for late 2016. On April 18, 2016, Swiss Pharma International AG filed petitions in the USPTO for inter partes review of U.S. Patent Nos. 8,349,321 and, 8,900,577, relating to specific formulations of natalizumab (TYSABRI), and U.S. Patent No. 8,815,236, relating to methods for treating multiple sclerosis and Crohn’s disease using specific formulations of natalizumab (TYSABRI). The USPTO has not yet decided whether to institute review. European Patent Office Oppositions On March 10, 2016, the European Patent Office verbally revoked our European patent number 2 137 537 (the '537 patent), which includes claims covering the treatment of multiple sclerosis with 480 mg of dimethyl fumarate as provided for in our TECFIDERA label. In June 2016 the European Patent Office issued a written decision confirming its position from which we intend to appeal. Patent Revocation Matter In December 2015, Swiss Pharma International AG brought an action in the Patents Court of the United Kingdom to revoke the UK counterpart of our European Patent Number 1 485 127 (“Administration of agents to treat inflammation”) (the '127 patent), which was issued in June 2011 and concerns administration of natalizumab (TYSABRI) to treat multiple sclerosis. The patent expires in February 2023. Subsequently, the same entity brought actions in the District Court of The Hague (on January 11, 2016) and the German Patents Court (on March 3, 2016) to invalidate the Dutch and German counterparts of the '127 patent. A hearing has been scheduled in the UK action for late 2016 and in the Dutch action for early 2017. No hearing has yet been scheduled in the German action. '755 Patent Litigation On May 28, 2010, Biogen MA Inc. (formerly Biogen Idec MA Inc.) filed a complaint in the U.S. District Court for the District of New Jersey alleging infringement by Bayer Healthcare Pharmaceuticals Inc. (Bayer) (manufacturer, marketer and seller of BETASERON and manufacturer of EXTAVIA), EMD Serono, Inc. (manufacturer, marketer and seller of REBIF), Pfizer Inc. (co-marketer of REBIF) and Novartis Pharmaceuticals Corp. (marketer and seller of EXTAVIA) of our U.S. Patent No. 7,588,755 ('755 Patent), which claims the use of interferon beta for immunomodulation or treating a viral condition, viral disease, cancers or tumors. The complaint seeks monetary damages, including lost profits and royalties. Bayer had previously filed a complaint against us in the same court, on May 27, 2010, seeking a declaratory judgment that it does not infringe the '755 Patent and that the patent is invalid, and seeking monetary relief in the form of attorneys' fees, costs and expenses. The court has consolidated the two lawsuits, and we refer to the two actions as the “Consolidated '755 Patent Actions.” Bayer, Pfizer, Novartis and EMD Serono have all filed counterclaims in the Consolidated '755 Patent Actions seeking declaratory judgments of patent invalidity and non-infringement, and seeking monetary relief in the form of costs and attorneys' fees, and EMD Serono and Bayer have each filed a counterclaim seeking a declaratory judgment that the '755 Patent is unenforceable based on alleged inequitable conduct. Bayer has also amended its complaint to seek such a declaration. Trial has been set for September 2017. Government Matters We have learned that state and federal governmental authorities are investigating our sales and promotional practices and have received related subpoenas. We are cooperating with the government. On March 4, 2016 we received a subpoena from the federal government for documents relating to our relationship with non-profit organizations that provide assistance to patients taking drugs sold by Biogen. We are cooperating with the government. On July 1, 2016, we received civil investigative demands from the federal government for documents and information relating to our treatment of certain service agreements with wholesalers when calculating and reporting Average Manufacturer Prices in connection with the Medicaid Drug Rebate Program. We are in the process of responding to the government. Product Liability and Other Legal Proceedings We are also involved in product liability claims and other legal proceedings generally incidental to our normal business activities. While the outcome of any of these proceedings cannot be accurately predicted, we do not believe the ultimate resolution of any of these existing matters would have a material adverse effect on our business or financial condition.

Commitments and Contingencies

Commitments and Contingencies	6 Months Ended
	Jun. 30, 2016
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies Disclosure	Commitments and Contingencies Fumapharm AG In 2006, we acquired Fumapharm AG. As part of this acquisition we acquired FUMADERM and TECFIDERA (together, Fumapharm Products). We paid $220.0 million upon closing of the transaction and agreed to pay an additional $15.0 million if a Fumapharm Product was approved for MS in the U.S. or E.U. In the second quarter of 2013, we paid this $15.0 million contingent payment as TECFIDERA was approved in the U.S. for MS by the FDA. We are also required to make additional contingent payments to former shareholders of Fumapharm AG or holders of their rights based on the attainment of certain cumulative sales levels of Fumapharm Products and the level of total net sales of Fumapharm Products in the prior twelve month period. During the six months ended June 30, 2016 , we paid $600.0 million in contingent payments as we reached the $7.0 billion and $8.0 billion cumulative sales levels related to the Fumapharm Products in the fourth quarter of 2015 and first quarter of 2016, respectively, and accrued $300.0 million upon reaching $9.0 billion in total cumulative sales of Fumapharm Products in the second quarter of 2016. We will owe an additional $300.0 million contingent payment for every additional $1.0 billion in cumulative sales level of Fumapharm Products reached if the prior 12 months sales of the Fumapharm Products exceed $3.0 billion , until such time as the cumulative sales level reaches $20.0 billion , at which time no further contingent payments shall be due. These payments will be accounted for as an increase to goodwill as incurred, in accordance with the accounting standard applicable to business combinations when we acquired Fumapharm. Any portion of the payment which is tax deductible will be recorded as a reduction to goodwill. Payments are due within 60 days following the end of the quarter in which the applicable cumulative sales level has been reached. Solothurn, Switzerland Facility On December 1, 2015, we purchased land in Solothurn, Switzerland where we are building a biologics manufacturing facility over the next several years. As of June 30, 2016 , we had contractual commitments of approximately $226.0 million for the construction of this facility.

Subsequent Events Subsequent Ev

Subsequent Events Subsequent Events	6 Months Ended
	Jun. 30, 2016
Subsequent Events [Abstract]
Subsequent Events	20. Subsequent Events On July 21, 2016, we announced that George A. Scangos, Ph.D. will step down as our Chief Executive Officer after a successor has been identified. Dr. Scangos will remain on our Board of Directors until he steps down from his executive position. Our Board of Directors will begin a search for Dr. Scangos’ successor immediately.

Summary of Significant Accoun27

Summary of Significant Accounting Policies Summary of Significant Accounting Policies (Policies)	6 Months Ended
	Jun. 30, 2016
Accounting Policies [Abstract]
Overview	Biogen is a global biopharmaceutical company focused on discovering, developing, manufacturing and delivering therapies to patients for the treatment of neurological diseases, autoimmune disorders and rare diseases. Our marketed products include TECFIDERA, AVONEX, PLEGRIDY, TYSABRI and FAMPYRA for multiple sclerosis (MS), ELOCTATE for hemophilia A and ALPROLIX for hemophilia B and FUMADERM for the treatment of severe plaque psoriasis. We also have a collaboration agreement with Genentech, Inc. (Genentech), a wholly-owned member of the Roche Group, which entitles us to certain business and financial rights with respect to RITUXAN for the treatment of non-Hodgkin's lymphoma, chronic lymphocytic leukemia (CLL) and other conditions, GAZYVA indicated for the treatment of CLL and follicular lymphoma, and other potential anti-CD20 therapies. In addition to our innovative drug development efforts, we aim to leverage our manufacturing capabilities and scientific expertise through Samsung Bioepis, our joint venture with Samsung BioLogics Co. Ltd. (Samsung Biologics) that develops, manufactures and markets biosimilars as well as through other strategic contract manufacturing partners. Under our commercial agreement with Samsung Bioepis, we market and sell BENEPALI, an etanercept biosimilar referencing ENBREL, and FLIXABI, an infliximab biosimilar referencing REMICADE, in the European Union (E.U.). In May 2016, we announced our intention to spin off our hemophilia business as an independent, publicly traded company. The new company will focus on the discovery and development of therapies for the treatment of hemophilia and other blood disorders, with existing marketed products ELOCTATE and ALPROLIX. The transaction is expected to be completed in early 2017, subject to the satisfaction of certain conditions, including, among others, final approval of our Board of Directors, receipt of a favorable opinion with respect to the tax-free nature of the transaction and the effectiveness of a Form 10 registration statement that will be filed with the Securities and Exchange Commission. The results of our hemophilia business will be included in our condensed consolidated financial statements until the transaction is completed.
Basis of presentation	In the opinion of management, the accompanying unaudited condensed consolidated financial statements include all adjustments, consisting of normal recurring accruals, necessary for a fair statement of our financial statements for interim periods in accordance with accounting principles generally accepted in the United States (U.S. GAAP). The information included in this quarterly report on Form 10-Q should be read in conjunction with our consolidated financial statements and the accompanying notes included in our Annual Report on Form 10-K for the year ended December 31, 2015 ( 2015 Form 10-K). Our accounting policies are described in the “ Notes to Consolidated Financial Statements ” in our 2015 Form 10-K and updated, as necessary, in this Form 10-Q. The year-end condensed consolidated balance sheet data presented for comparative purposes was derived from our audited financial statements, but does not include all disclosures required by U.S. GAAP. The results of operations for the three and six months ended June 30, 2016 , are not necessarily indicative of the operating results for the full year or for any other subsequent interim period. We operate as one operating segment, which is discovering, developing, manufacturing and delivering therapies to patients for the treatment of neurological diseases, autoimmune disorders and rare diseases.
Consolidation	Our condensed consolidated financial statements reflect our financial statements, those of our wholly-owned subsidiaries and those of certain variable interest entities where we are the primary beneficiary. For consolidated entities where we own or are exposed to less than 100% of the economics, we record net income (loss) attributable to noncontrolling interests in our condensed consolidated statements of income equal to the percentage of the economic or ownership interest retained in such entities by the respective noncontrolling parties. Intercompany balances and transactions are eliminated in consolidation. In determining whether we are the primary beneficiary of an entity, we apply a qualitative approach that determines whether we have both (1) the power to direct the economically significant activities of the entity and (2) the obligation to absorb losses of, or the right to receive benefits from, the entity that could potentially be significant to that entity. These considerations impact the way we account for our existing collaborative relationships and other arrangements. We continuously assess whether we are the primary beneficiary of a variable interest entity as changes to existing relationships or future transactions may result in us consolidating or deconsolidating one or more of our collaborators or partners.
Use of estimates	The preparation of our condensed consolidated financial statements requires us to make estimates, judgments and assumptions that may affect the reported amounts of assets, liabilities, equity, revenues and expenses and related disclosure of contingent assets and liabilities. On an on-going basis we evaluate our estimates, judgments and methodologies. We base our estimates on historical experience and on various other assumptions that we believe to be reasonable, the results of which form the basis for making judgments about the carrying values of assets, liabilities and equity and the amount of revenues and expenses. Actual results may differ from these estimates under different assumptions or conditions.
New accounting pronouncements	From time to time, new accounting pronouncements are issued by the Financial Accounting Standards Board (FASB) or other standard setting bodies that we adopt as of the specified effective date. Unless otherwise discussed, we do not believe that the impact of recently issued standards that are not yet effective will have a material impact on our financial position or results of operations upon adoption. In May 2014, the FASB issued Accounting Standards Update (ASU) No. 2014-09, Revenue from Contracts with Customers (Topic 606), which supersedes all existing revenue recognition requirements, including most industry-specific guidance. The new standard requires a company to recognize revenue when it transfers goods or services to customers in an amount that reflects the consideration that the company expects to receive for those goods or services. In August 2015, the FASB issued ASU No. 2015-14, Revenue from Contracts with Customers (Topic 606): Deferral of the Effective Date, which delayed the effective date of the new standard from January 1, 2017 to January 1, 2018. The FASB also agreed to allow entities to choose to adopt the standard as of the original effective date. In March 2016, the FASB issued ASU No. 2016-08, Revenue from Contracts with Customers (Topic 606): Principal versus Agent Considerations, which clarifies the implementation guidance on principal versus agent considerations. In April 2016, the FASB issued ASU No. 2016-10, Revenue from Contracts with Customers (Topic 606): Identifying Performance Obligations and Licensing, which clarifies certain aspects of identifying performance obligations and licensing implementation guidance. In May 2016, the FASB issued ASU No. 2016-12, Revenue from Contracts with Customers (Topic 606): Narrow-Scope Improvements and Practical Expedients related to disclosures of remaining performance obligations, as well as other amendments to guidance on collectibility, non-cash consideration and the presentation of sales and other similar taxes collected from customers. These standards have the same effective date and transition date of January 1, 2018. We are currently evaluating the method of adoption and the potential impact that these standards may have on our financial position and results of operations. During 2015, the FASB issued the following new standards, which we adopted on January 1, 2016: • ASU No. 2015-05, Intangibles - Goodwill and Other - Internal-Use Software (Subtopic 350-40): Customer's Accounting for Fees Paid in a Cloud Computing Arrangement. • ASU No. 2015-11, Inventory (Topic 330): Simplifying the Measurement of Inventory. • ASU No. 2015-16, Business Combinations (Topic 805): Simplifying the Accounting for Measurement-Period Adjustments. The adoption of these standards did not have an impact on our financial position or results of operations. For additional information related to these standards, please read Note 1, Summary of Significant Accounting Policies: New Accounting Pronouncements to our consolidated financial statements included in our 2015 Form 10-K. In January 2016, the FASB issued ASU No. 2016-01, Financial Instruments - Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities. The new standard amends certain aspects of accounting and disclosure requirements of financial instruments, including the requirement that equity investments with readily determinable fair values be measured at fair value with changes in fair value recognized in our results of operations. The new standard does not apply to investments accounted for under the equity method of accounting or those that result in consolidation of the investee. Equity investments that do not have readily determinable fair values may be measured at fair value or at cost minus impairment adjusted for changes in observable prices. A financial liability that is measured at fair value in accordance with the fair value option is required to be presented separately in other comprehensive income for the portion of the total change in the fair value resulting from change in the instrument-specific credit risk. In addition, a valuation allowance should be evaluated on deferred tax assets related to available-for-sale debt securities in combination with other deferred tax assets. The new standard will be effective for us on January 1, 2018. The adoption of this standard is not expected to have a material impact on our financial position or results of operations. In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842). The new standard requires that all lessees recognize the assets and liabilities that arise from leases on the balance sheet and disclose qualitative and quantitative information about its leasing arrangements. The new standard will be effective for us on January 1, 2019. The adoption of this standard is not expected to have a material impact on our net financial position, but will impact our assets and liabilities. We are currently evaluating the potential impact that this standard may have on our results of operations. In March 2016, the FASB issued ASU No. 2016-06, Derivatives and Hedging (Topic 815): Contingent Put and Call Options in Debt Instruments. The new standard simplifies the embedded derivative analysis for debt instruments containing contingent call or put options by removing the requirement to assess whether a contingent event is related to interest rates or credit risks. The new standard will be effective for us on January 1, 2017. The adoption of this standard is not expected to have an impact on our financial position or results of operations. In March 2016, the FASB issued ASU No. 2016-07, Investments - Equity Method and Joint Ventures (Topic 323): Simplifying the Transition to the Equity Method of Accounting. The new standard eliminates the requirement that when an investment qualifies for use of the equity method as a result of an increase in the level of ownership interest or degree of influence, an adjustment must be made to the investment, results of operations and retained earnings retroactively on a step-by-step basis as if the equity method had been in effect during all previous periods that the investment had been held. The new standard will be effective for us on January 1, 2017. The adoption of this standard is not expected to have a material impact on our financial position or results of operations. In March 2016, the FASB issued ASU No. 2016-09, Compensation - Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting. The new standard requires recognition of the income tax effects of vested or settled awards in the income statement and involves several other aspects of the accounting for share-based payment transactions, including the income tax consequences, classification of awards as either equity or liabilities and classification on the statement of cash flows. The new standard will be effective for us on January 1, 2017. This standard is not expected to have a material impact on our financial position, results of operations or statements of cash flows upon adoption. In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments. The new standard changes the impairment model for most financial assets and certain other instruments. Under the new standard, entities holding financial assets and net investment in leases that are not accounted for at fair value through net income to be presented at the net amount expected to be collected. An allowance for credit losses will be a valuation account that will be deducted from the amortized cost basis of the financial asset to present the net carrying value at the amount expected to be collected on the financial asset. The new standard will be effective for us on January 1, 2020. The adoption of this standard is not expected to have a material impact on our financial position or results of operations.

Restructuring Restructuring (Ta

Restructuring Restructuring (Tables)	6 Months Ended
	Jun. 30, 2016
Restructuring and Related Activities [Abstract]
Charges and spending related to our restructuring efforts	The following table summarizes the charges and spending related to our restructuring efforts during the six months ended June 30, 2016 : (In millions) Workforce Reduction Pipeline Programs Total Restructuring reserve as of December 31, 2015 $ 33.7 $ 3.6 $ 37.3 Expense 4.9 5.4 10.3 Payments (28.7 ) (6.0 ) (34.7 ) Adjustments to previous estimates, net (3.5 ) 2.9 (0.6 ) Restructuring reserve as of June 30, 2016 $ 6.4 $ 5.9 $ 12.3

Reserves for Discounts and Al29

Reserves for Discounts and Allowances (Tables)	6 Months Ended
	Jun. 30, 2016
Sales Discounts, Returns and Allowances, Goods [Abstract]
Analysis of the changes in reserves	An analysis of the change in reserves for discounts and allowances is summarized as follows: (In millions) Discounts Contractual Adjustments Returns Total Balance, as of December 31, 2015 $ 56.1 $ 548.7 $ 57.9 $ 662.7 Current provisions relating to sales in current year 266.8 973.8 17.6 1,258.2 Adjustments relating to prior years (2.4 ) 1.6 (5.5 ) (6.3 ) Payments/credits relating to sales in current year (210.2 ) (605.1 ) (0.7 ) (816.0 ) Payments/credits relating to sales in prior years (51.5 ) (384.9 ) (10.4 ) (446.8 ) Balance, as of June 30, 2016 $ 58.8 $ 534.1 $ 58.9 $ 651.8
Total reserves included in condensed consolidated balance sheets	The total reserves above, included in our condensed consolidated balance sheets, are summarized as follows: (In millions) As of As of Reduction of accounts receivable $ 161.3 $ 144.6 Component of accrued expenses and other 490.5 518.1 Total reserves $ 651.8 $ 662.7

Inventory (Tables)

Inventory (Tables)	6 Months Ended
	Jun. 30, 2016
Inventory Disclosure [Abstract]
Components of inventory	The components of inventory are summarized as follows: (In millions) As of As of Raw materials $ 235.0 $ 213.0 Work in process 654.6 577.6 Finished goods 139.1 143.0 Total inventory $ 1,028.7 $ 933.6 Balance Sheet Classification: Inventory $ 996.4 $ 893.4 Investments and other assets 32.3 40.2 Total inventory $ 1,028.7 $ 933.6

Intangible Assets and Goodwill

Intangible Assets and Goodwill (Tables)	6 Months Ended
	Jun. 30, 2016
Goodwill and Intangible Assets Disclosure [Abstract]
Intangible assets	Intangible assets, net of accumulated amortization, impairment charges and adjustments, are summarized as follows: As of June 30, 2016 As of December 31, 2015 (In millions) Estimated Life Cost Accumulated Amortization Net Cost Accumulated Amortization Net Out-licensed patents 13-23 years $ 543.3 $ (514.9 ) $ 28.4 $ 543.3 $ (506.0 ) $ 37.3 Developed technology 15-23 years 3,005.3 (2,604.5 ) 400.8 3,005.3 (2,552.9 ) 452.4 In-process research and development Indefinite until commercialization 692.3 — 692.3 730.5 — 730.5 Trademarks and tradenames Indefinite 64.0 — 64.0 64.0 — 64.0 Acquired and in-licensed rights and patents 6-18 years 3,405.4 (623.3 ) 2,782.1 3,303.2 (502.3 ) 2,800.9 Total intangible assets $ 7,710.3 $ (3,742.7 ) $ 3,967.6 $ 7,646.3 $ (3,561.2 ) $ 4,085.1
Estimated future amortization for acquired intangible assets	Based upon this analysis, the estimated future amortization of acquired intangible assets for the next five years is expected to be as follows: (In millions) As of 2016 (remaining six months) $ 181.6 2017 325.1 2018 298.2 2019 282.7 2020 277.1 2021 265.0
Summary of roll forward of the changes in goodwill	The following table provides a roll forward of the changes in our goodwill balance: (In millions) As of Goodwill, beginning of period $ 2,663.8 Increase to goodwill 515.0 Other (11.7 ) Goodwill, end of period $ 3,167.1

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	6 Months Ended
	Jun. 30, 2016
Fair Value Disclosures [Abstract]
Summary of assets and liabilities recorded at fair value	The tables below present information about our assets and liabilities that are regularly measured and carried at fair value and indicate the level within the fair value hierarchy of the valuation techniques we utilized to determine such fair value: As of June 30, 2016 (In millions) Total Quoted Prices in Active Markets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Assets: Cash equivalents $ 874.6 $ — $ 874.6 $ — Marketable debt securities: Corporate debt securities 2,290.3 — 2,290.3 — Government securities 2,973.4 — 2,973.4 — Mortgage and other asset backed securities 648.7 — 648.7 — Marketable equity securities 32.4 32.4 — — Derivative contracts 30.1 — 30.1 — Plan assets for deferred compensation 35.6 — 35.6 — Total $ 6,885.1 $ 32.4 $ 6,852.7 $ — Liabilities: Derivative contracts $ 24.8 $ — $ 24.8 $ — Contingent consideration obligations 515.7 — — 515.7 Total $ 540.5 $ — $ 24.8 $ 515.7 As of December 31, 2015 (In millions) Total Quoted Prices in Active Markets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Assets: Cash equivalents $ 909.5 $ — $ 909.5 $ — Marketable debt securities: Corporate debt securities 1,510.9 — 1,510.9 — Government securities 2,875.9 — 2,875.9 — Mortgage and other asset backed securities 494.1 — 494.1 — Marketable equity securities 37.5 37.5 — — Derivative contracts 27.2 — 27.2 — Plan assets for deferred compensation 40.1 — 40.1 — Total $ 5,895.2 $ 37.5 $ 5,857.7 $ — Liabilities: Derivative contracts $ 14.7 $ — $ 14.7 $ — Contingent consideration obligations 506.0 — — 506.0 Total $ 520.7 $ — $ 14.7 $ 506.0
Summary of fair and carrying value of debt instruments	The fair and carrying values of our debt instruments, which are Level 2 liabilities, are summarized as follows: As of June 30, 2016 As of December 31, 2015 (In millions) Fair Value Carrying Value Fair Value Carrying Value Notes payable to Fumedica $ 6.4 $ 6.1 $ 9.4 $ 9.0 6.875% Senior Notes due March 1, 2018 598.2 561.9 602.6 565.3 2.900% Senior Notes due September 15, 2020 1,561.7 1,507.9 1,497.5 1,485.5 3.625% Senior Notes due September 15, 2022 1,061.0 992.7 1,014.2 992.2 4.050% Senior Notes due September 15, 2025 1,887.3 1,734.1 1,764.6 1,733.4 5.200% Senior Notes due September 15, 2045 1,996.3 1,721.3 1,757.6 1,721.1 Total $ 7,110.9 $ 6,524.0 $ 6,645.9 $ 6,506.5
Fair value of contingent consideration obligations	The following table provides a roll forward of the fair values of our contingent consideration obligations which includes Level 3 measurements: For the Three Months For the Six Months (In millions) 2016 2015 2016 2015 Fair value, beginning of period $ 508.3 $ 461.8 $ 506.0 $ 215.5 Additions — 36.0 — 274.5 Changes in fair value 10.6 (2.2 ) 12.9 5.6 Payments (3.2 ) — (3.2 ) — Fair value, end of period $ 515.7 $ 495.6 $ 515.7 $ 495.6

Financial Instruments (Tables)

Financial Instruments (Tables)	6 Months Ended
	Jun. 30, 2016
Investments, Debt and Equity Securities [Abstract]
Summary of financial assets with maturities of less than 90 days included within cash and cash equivalents	The following table summarizes our financial assets with maturities of less than 90 days from the date of purchase included in cash and cash equivalents on the accompanying condensed consolidated balance sheet: (In millions) As of As of Commercial paper $ 56.9 $ 21.9 Overnight reverse repurchase agreements 66.3 134.7 Money market funds 531.5 673.8 Short-term debt securities 219.9 79.1 Total $ 874.6 $ 909.5
Marketable debt and equity securities	The following tables summarize our marketable debt and equity securities, classified as available-for-sale: As of June 30, 2016 (In millions) Fair Value Gross Unrealized Gains Gross Unrealized Losses Amortized Cost Corporate debt securities Current $ 913.4 $ 0.3 $ (0.2 ) $ 913.3 Non-current 1,376.9 7.8 (0.4 ) 1,369.5 Government securities Current 1,521.3 0.6 — 1,520.7 Non-current 1,452.1 3.1 (0.6 ) 1,449.6 Mortgage and other asset backed securities Current 0.1 — — 0.1 Non-current 648.6 1.4 (0.9 ) 648.1 Total marketable debt securities $ 5,912.4 $ 13.2 $ (2.1 ) $ 5,901.3 Marketable equity securities, non-current $ 32.4 $ 0.9 $ (2.1 ) $ 33.6 As of December 31, 2015 (In millions) Fair Value Gross Unrealized Gains Gross Unrealized Losses Amortized Cost Corporate debt securities Current $ 394.3 $ — $ (0.5 ) $ 394.8 Non-current 1,116.6 0.1 (4.1 ) 1,120.6 Government securities Current 1,723.4 0.1 (1.1 ) 1,724.4 Non-current 1,152.5 — (3.1 ) 1,155.6 Mortgage and other asset backed securities Current 2.8 — — 2.8 Non-current 491.3 0.1 (1.8 ) 493.0 Total marketable debt securities $ 4,880.9 $ 0.3 $ (10.6 ) $ 4,891.2 Marketable equity securities, non-current $ 37.5 $ 9.2 $ — $ 28.3
Summary of contractual maturities: available-for-sale securities	The estimated fair value and amortized cost of our marketable debt securities available-for-sale by contractual maturity are summarized as follows: As of June 30, 2016 As of December 31, 2015 (In millions) Estimated Fair Value Amortized Cost Estimated Fair Value Amortized Cost Due in one year or less $ 2,434.8 $ 2,434.1 $ 2,120.5 $ 2,122.0 Due after one year through five years 3,255.9 3,245.4 2,575.9 2,583.9 Due after five years 221.7 221.8 184.5 185.3 Total available-for-sale securities $ 5,912.4 $ 5,901.3 $ 4,880.9 $ 4,891.2
Proceeds from marketable debt securities	The proceeds from maturities and sales of marketable debt securities and resulting realized gains and losses are summarized as follows: For the Three Months For the Six Months (In millions) 2016 2015 2016 2015 Proceeds from maturities and sales $ 1,642.5 $ 601.9 $ 2,823.6 $ 975.5 Realized gains $ 0.6 $ 0.3 $ 1.0 $ 0.5 Realized losses $ (1.2 ) $ (0.5 ) $ (1.6 ) $ (0.8 )

Derivative Instruments (Tables)

Derivative Instruments (Tables)	6 Months Ended
	Jun. 30, 2016
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Foreign currency forward contracts that were entered into to hedge forecasted revenue	The notional value of foreign currency forward contracts that were entered into to hedge forecasted revenues and operating expenses is summarized as follows: Notional Amount Foreign Currency: (In millions) As of As of Euro $ 1,126.5 $ 945.5 Swiss francs 43.5 80.8 Canadian dollar 39.9 76.7 Total foreign currency forward contracts $ 1,209.9 $ 1,103.0
Summary of the effect of derivatives designated as hedging instruments on the condensed consolidated statements of income	The following tables summarize the effect of foreign currency forward contracts designated as hedging instruments on our condensed consolidated statements of income: For the Three Months Ended June 30, Net Gains/(Losses) Reclassified from AOCI into Operating Income (Effective Portion) Net Gains/(Losses) Recognized into Net Income (Ineffective Portion) Location 2016 2015 Location 2016 2015 Revenue $ (4.3 ) $ 40.4 Other income (expense) $ 2.1 $ 1.2 Operating expenses $ (0.1 ) $ — Other income (expense) $ — $ — For the Six Months Ended June 30, Net Gains/(Losses) Reclassified from AOCI into Operating Income (Effective Portion) Net Gains/(Losses) Recognized into Net Income (Ineffective Portion) Location 2016 2015 Location 2016 2015 Revenue $ 4.5 $ 75.4 Other income (expense) $ 4.0 $ 3.4 Operating expenses $ (0.2 ) $ — Other income (expense) $ (0.3 ) $ —
Summary of fair value and presentation of derivatives	The following table summarizes the fair value and presentation in our condensed consolidated balance sheets of our outstanding derivatives including those designated as hedging instruments: Fair Value (In millions) Balance Sheet Location As of June 30, 2016 Hedging Instruments: Asset derivatives Other current assets $ 2.0 Investments and other assets $ 23.6 Liability derivatives Accrued expenses and other $ 14.8 Other long-term liabilities $ — Other Derivatives: Asset derivatives Other current assets $ 4.5 Liability derivatives Accrued expenses and other $ 10.0 Fair Value (In millions) Balance Sheet Location As of December 31, 2015 Hedging Instruments: Asset derivatives Other current assets $ 16.6 Investments and other assets $ 0.3 Liability derivatives Accrued expenses and other $ 10.2 Other long-term liabilities $ 2.5 Other Derivatives: Asset derivatives Other current assets $ 10.3 Liability derivatives Accrued expenses and other $ 2.0

Equity (Tables)

Equity (Tables)	6 Months Ended
	Jun. 30, 2016
Equity [Abstract]
Reconciliation of equity attributable to noncontrolling interests	The following table reconciles equity (deficit) attributable to noncontrolling interests (NCI): For the Three Months For the Six Months (In millions) 2016 2015 2016 2015 NCI, beginning of period $ 1.3 $ 2.7 $ 2.1 $ 5.0 Net income (loss) attributable to NCI, net of tax (1.4 ) (2.5 ) (3.1 ) (4.8 ) Fair value of net assets and liabilities acquired and assigned to NCI — — 0.9 — Translation adjustment and other — 0.2 — 0.2 NCI, end of period $ (0.1 ) $ 0.4 $ (0.1 ) $ 0.4

Accumulated Other Comprehensi36

Accumulated Other Comprehensive Income (Loss) Accumulated Other Comprehensive Income (Loss) (Tables)	6 Months Ended
	Jun. 30, 2016
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Schedule of accumulated other comprehensive income (loss)	The following table summarizes the changes in accumulated other comprehensive income (loss), net of tax by component: (In millions) Unrealized Gains (Losses) on Securities Available for Sale Unrealized Gains (Losses) on Cash Flow Hedges Unfunded Status of Postretirement Benefit Plans Translation Adjustments Total Balance, as of December 31, 2015 $ (0.8 ) $ 10.2 $ (37.8 ) $ (195.6 ) $ (224.0 ) Other comprehensive income (loss) before reclassifications 6.6 (13.9 ) 0.9 (48.4 ) (54.8 ) Amounts reclassified from accumulated other comprehensive income (loss) 0.4 (4.4 ) — — (4.0 ) Net current period other comprehensive income (loss) 7.0 (18.3 ) 0.9 (48.4 ) (58.8 ) Balance, as of June 30, 2016 $ 6.2 $ (8.1 ) $ (36.9 ) $ (244.0 ) $ (282.8 ) (In millions) Unrealized Gains (Losses) on Securities Available for Sale Unrealized Gains (Losses) on Cash Flow Hedges Unfunded Status of Postretirement Benefit Plans Translation Adjustments Total Balance, as of December 31, 2014 $ (0.4 ) $ 71.7 $ (31.6 ) $ (99.2 ) $ (59.5 ) Other comprehensive income (loss) before reclassifications 0.9 66.1 4.1 (37.8 ) 33.3 Amounts reclassified from accumulated other comprehensive income (loss) 0.2 (75.0 ) — — (74.8 ) Net current period other comprehensive income (loss) 1.1 (8.9 ) 4.1 (37.8 ) (41.5 ) Balance, as of June 30, 2015 $ 0.7 $ 62.8 $ (27.5 ) $ (137.0 ) $ (101.0 )
Reclassification out of accumulated other comprehensive income	The following table summarizes the amounts reclassified from accumulated other comprehensive income: (In millions) Income Statement Location Amounts Reclassified from Accumulated Other Comprehensive Income For the Three Months For the Six Months 2016 2015 2016 2015 Gains (losses) on securities available for sale Other income (expense) $ (0.6 ) $ (0.2 ) $ (0.6 ) $ (0.3 ) Income tax benefit (expense) 0.2 0.1 0.2 0.1 Gains (losses) on cash flow hedges Revenues (4.3 ) 40.4 4.5 75.4 Operating expenses (0.1 ) — (0.2 ) — Other income (expense) — — 0.1 — Income tax benefit (expense) 0.1 (0.2 ) — (0.4 ) Total reclassifications, net of tax $ (4.7 ) $ 40.1 $ 4.0 $ 74.8

Earnings per Share (Tables)

Earnings per Share (Tables)	6 Months Ended
	Jun. 30, 2016
Earnings Per Share [Abstract]
Basic and diluted earnings per share	Basic and diluted earnings per share are calculated as follows: For the Three Months For the Six Months (In millions) 2016 2015 2016 2015 Numerator: Net income attributable to Biogen Inc. $ 1,049.8 $ 927.3 $ 2,020.7 $ 1,749.8 Denominator: Weighted average number of common shares outstanding 219.1 235.3 219.0 235.1 Effect of dilutive securities: Stock options and employee stock purchase plan 0.1 0.1 0.1 0.1 Time-vested restricted stock units 0.1 0.2 0.1 0.3 Market stock units 0.1 0.1 0.1 0.2 Dilutive potential common shares 0.3 0.4 0.3 0.6 Shares used in calculating diluted earnings per share 219.4 235.7 219.3 235.7

Share-Based Payments (Tables)

Share-Based Payments (Tables)	6 Months Ended
	Jun. 30, 2016
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Share-based compensation expense included in condensed consolidated statements of income	The following table summarizes share-based compensation expense included in our condensed consolidated statements of income: For the Three Months For the Six Months (In millions) 2016 2015 2016 2015 Research and development $ 21.5 $ 22.1 $ 42.9 $ 57.5 Selling, general and administrative 28.7 26.2 63.4 81.8 Restructuring charges — — (1.8 ) — Subtotal 50.2 48.3 104.5 139.3 Capitalized share-based compensation costs (4.4 ) (2.2 ) (7.5 ) (5.6 ) Share-based compensation expense included in total cost and expenses 45.8 46.1 97.0 133.7 Income tax effect (12.7 ) (12.9 ) (27.9 ) (39.6 ) Share-based compensation expense included in net income attributable to Biogen Inc. $ 33.1 $ 33.2 $ 69.1 $ 94.1
Summary of share-based compensation expense associated with each of our share-based compensating programs	The following table summarizes share-based compensation expense associated with each of our share-based compensation programs: For the Three Months For the Six Months (In millions) 2016 2015 2016 2015 Market stock units $ 7.9 $ 9.1 $ 21.3 26.1 Time-vested restricted stock units 33.9 31.8 64.0 63.7 Cash settled performance units 4.6 3.2 4.8 27.0 Performance units 1.3 1.2 8.2 14.4 Employee stock purchase plan 2.5 3.0 6.2 8.1 Subtotal 50.2 48.3 104.5 139.3 Capitalized share-based compensation costs (4.4 ) (2.2 ) (7.5 ) (5.6 ) Share-based compensation expense included in total cost and expenses $ 45.8 $ 46.1 $ 97.0 $ 133.7
Summary of equity grants to employees, officers and directors under our current stock plans	The following table summarizes our equity grants to employees, officers and directors under our current stock plans: For the Six Months 2016 2015 Market stock units 166,000 179,000 Cash settled performance shares 86,000 115,000 Performance units 56,000 89,000 Time-vested restricted stock units 594,000 375,000

Income Taxes (Tables)

Income Taxes (Tables)	6 Months Ended
	Jun. 30, 2016
Income Tax Disclosure [Abstract]
Reconciliation between the U.S. federal statutory tax rate and effective tax rate	A reconciliation between the U.S. federal statutory tax rate and our effective tax rate is summarized as follows: For the Three Months For the Six Months 2016 2015 2016 2015 Statutory rate 35.0 % 35.0 % 35.0 % 35.0 % State taxes 1.0 0.4 1.0 — Taxes on foreign earnings (10.0 ) (11.1 ) (9.0 ) (9.8 ) Credits and net operating loss utilization (1.2 ) (0.7 ) (1.2 ) (0.7 ) Purchased intangible assets 1.1 1.1 1.1 1.0 Manufacturing deduction (1.6 ) (2.1 ) (1.7 ) (1.8 ) Other permanent items 0.6 0.9 0.6 0.7 Other 0.3 0.4 0.2 0.3 Effective tax rate 25.2 % 23.9 % 26.0 % 24.7 %

Other Consolidated Financial 40

Other Consolidated Financial Statement Detail (Tables)	6 Months Ended
	Jun. 30, 2016
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Other income (expense), net	Components of other income (expense), net, are summarized as follows: For the Three Months For the Six Months (In millions) 2016 2015 2016 2015 Interest income $ 15.4 $ 4.3 $ 26.6 $ 7.6 Interest expense (65.9 ) (5.8 ) (129.2 ) (12.5 ) Gain (loss) on investments, net (2.7 ) 0.3 (1.1 ) (1.4 ) Foreign exchange gains (losses), net 0.2 (1.5 ) 2.3 (14.5 ) Other, net (5.5 ) (8.2 ) (9.9 ) (5.1 ) Total other income (expense), net $ (58.5 ) $ (10.9 ) $ (111.3 ) $ (25.9 )
Accrued expenses and other	Accrued expenses and other consists of the following: (In millions) As of As of Current portion of contingent consideration obligations and milestones $ 556.7 $ 504.7 Revenue-related reserves for discounts and allowances 490.5 518.1 Employee compensation and benefits 228.4 270.8 Royalties and licensing fees 183.7 167.9 Other 613.4 635.3 Total accrued expenses and other $ 2,072.7 $ 2,096.8

Collaborative and Other Relat41

Collaborative and Other Relationships Collaborative and Other Relationships (Tables)	6 Months Ended
	Jun. 30, 2016
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Cash reimbursement as an adjustment to the Base Rate	We expect to recognize the effect of the cash reimbursement as an adjustment to the Base Rate in the table below over a ten year period, consistent with the initial patent term of the products. Under the collaboration agreement, cash payments are as follows: Rates post Sobi Opt-In (3) Royalty and Net Revenue Share Rates: Method Base Rate following 1st commercial sale in the Sobi Territory: Rate during the Reimbursement Period: Sobi rate to Biogen on net sales in the Sobi Territory Royalty 12% Base Rate Biogen rate to Sobi on net sales in the Biogen North America Territory Royalty 12% Base Rate Biogen rate to Sobi on net sales in the Biogen Direct Territory Royalty 17% Base Rate Biogen rate to Sobi on net revenue (1) from the Biogen Distributor Territory (2) Net 50% Base Rate

Summary of Significant Accoun42

Summary of Significant Accounting Policies Summary of Significant Accounting Policies (Details)	6 Months Ended
	Jun. 30, 2016segment
Accounting Policies [Abstract]
Number of reportable segments	1
Interest in subsidiary (less than given percentage)	100.00%

Restructuring Restructuring (De

Restructuring Restructuring (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Dec. 31, 2015	Jun. 30, 2016
Restructuring Cost and Reserve [Line Items]
Restructuring reserve as of December 31, 2015		$ 37.3
Expense		10.3
Payments		(34.7)
Adjustments to previous estimates, net		(0.6)
Restructuring reserve as of June 30, 2016	$ 37.3	12.3
Workforce reduction
Restructuring Cost and Reserve [Line Items]
Restructuring reserve as of December 31, 2015		33.7
Expense		4.9
Payments		(28.7)
Adjustments to previous estimates, net	15.9	(3.5)
Restructuring reserve as of June 30, 2016	33.7	6.4
Pipeline programs
Restructuring Cost and Reserve [Line Items]
Restructuring reserve as of December 31, 2015		3.6
Expense		5.4
Payments		(6)
Adjustments to previous estimates, net		2.9
Restructuring reserve as of June 30, 2016	$ 3.6	$ 5.9

Restructuring Restructuring (44

Restructuring Restructuring (Details Textual) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2016	Dec. 31, 2015	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Restructuring Cost and Reserve [Line Items]
Expected cash payments	$ 120			$ 120
Adjustments to previous estimates, net				(0.6)
Expected restructuring charges	105			105
Restructuring charges	$ 0	$ 93.4	$ 0	9.7	$ 0
Workforce reduction
Restructuring Cost and Reserve [Line Items]
Restructuring and related cost, expected percentage of positions eliminated		11.00%
Adjustments to previous estimates, net		$ 15.9		$ (3.5)

Reserves for Discounts and Al45

Reserves for Discounts and Allowances (Details) $ in Millions	6 Months Ended
	Jun. 30, 2016USD ($)
Analysis of the amount of, and change in, reserves
Balance as of December 31, 2015	$ 662.7
Current provisions relating to sales in current year	1,258.2
Adjustments relating to prior years	(6.3)
Payments/credits relating to sales in current year	(816)
Payments/credits relating to sales in prior years	(446.8)
Balance as of June 30, 2016	651.8
Discounts
Analysis of the amount of, and change in, reserves
Balance as of December 31, 2015	56.1
Current provisions relating to sales in current year	266.8
Adjustments relating to prior years	(2.4)
Payments/credits relating to sales in current year	(210.2)
Payments/credits relating to sales in prior years	(51.5)
Balance as of June 30, 2016	58.8
Contractual Adjustments
Analysis of the amount of, and change in, reserves
Balance as of December 31, 2015	548.7
Current provisions relating to sales in current year	973.8
Adjustments relating to prior years	1.6
Payments/credits relating to sales in current year	(605.1)
Payments/credits relating to sales in prior years	(384.9)
Balance as of June 30, 2016	534.1
Returns
Analysis of the amount of, and change in, reserves
Balance as of December 31, 2015	57.9
Current provisions relating to sales in current year	17.6
Adjustments relating to prior years	(5.5)
Payments/credits relating to sales in current year	(0.7)
Payments/credits relating to sales in prior years	(10.4)
Balance as of June 30, 2016	$ 58.9

Reserves for Discounts and Al46

Reserves for Discounts and Allowances (Details 1) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015
Summary of total product revenue reserves included in consolidated balance sheets
Total reserves	$ 651.8	$ 662.7
Reduction of accounts receivable
Summary of total product revenue reserves included in consolidated balance sheets
Total reserves	161.3	144.6
Component of accrued expenses and other
Summary of total product revenue reserves included in consolidated balance sheets
Total reserves	$ 490.5	$ 518.1

Inventory (Details)

Inventory (Details) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015
Components of inventories
Raw materials	$ 235	$ 213
Work in process	654.6	577.6
Finished goods	139.1	143
Total inventory	1,028.7	933.6
Inventory, current	996.4	893.4
Inventory, Noncurrent	$ 32.3	$ 40.2

Inventory Inventory (Details Te

Inventory Inventory (Details Textual) $ in Millions	Dec. 31, 2015USD ($)
ZINBRYTA
Inventory [Line Items]
Pre-approval inventory	$ 24.7
FLIXABI
Inventory [Line Items]
Pre-approval inventory	24.2
BENEPALI
Inventory [Line Items]
Pre-approval inventory	$ 18.4

Intangible Assets and Goodwil49

Intangible Assets and Goodwill (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Intangible assets
Total intangible assets, gross	$ 7,710.3		$ 7,710.3		$ 7,646.3
Accumulated Amortization	(3,742.7)		(3,742.7)		(3,561.2)
Intangible assets, net	3,967.6		3,967.6		4,085.1
Intangible Assets and Goodwill (Textual) [Abstract]
Amortization of acquired intangible assets	92.9	$ 92	181.7	$ 187.9
Accumulated impairment losses related to goodwill	0		0
Expected future amortization expense, 2016 (remaining six months)	181.6		181.6
Expected future amortization expense, 2017	325.1		325.1
Expected future amortization expense, 2018	298.2		298.2
Expected future amortization expense, 2019	282.7		282.7
Expected future amortization expense, 2020	277.1		277.1
Expected future amortization expense, 2021	265		265
Out-licensed patents
Intangible assets
Cost	543.3		543.3		543.3
Accumulated Amortization	(514.9)		(514.9)		(506)
Net	28.4		$ 28.4		37.3
Out-licensed patents | Minimum
Intangible assets
Estimated life, (in years)			13 years
Out-licensed patents | Maximum
Intangible assets
Estimated life, (in years)			23 years
Developed technology
Intangible assets
Cost	3,005.3		$ 3,005.3		3,005.3
Accumulated Amortization	(2,604.5)		(2,604.5)		(2,552.9)
Net	400.8		$ 400.8		452.4
Developed technology | Minimum
Intangible assets
Estimated life, (in years)			15 years
Developed technology | Maximum
Intangible assets
Estimated life, (in years)			23 years
Developed technology | AVONEX
Intangible assets
Net	392.8		$ 392.8
Acquired and in-licensed rights and patents
Intangible assets
Cost	3,405.4		3,405.4		3,303.2
Accumulated Amortization	(623.3)		(623.3)		(502.3)
Net	2,782.1		$ 2,782.1		2,800.9
Acquired and in-licensed rights and patents | Minimum
Intangible assets
Estimated life, (in years)			6 years
Acquired and in-licensed rights and patents | Maximum
Intangible assets
Estimated life, (in years)			18 years
Acquired and in-licensed rights and patents | Biosimilars
Intangible assets
Increase in acquired and in-licensed rights and patents	25		$ 50
Acquired and in-licensed rights and patents | ZINBRYTA
Intangible assets
Increase in acquired and in-licensed rights and patents			20
Acquired and in-licensed rights and patents | ALPROLIX
Intangible assets
Increase in acquired and in-licensed rights and patents			26.5
Contingent payment made during the period			20
Deferred tax liability	6.5		$ 6.5
In-process research and development
Intangible assets
Indefinite lived intangible assets useful life			Indefinite until commercialization
Cost and Net	692.3		$ 692.3		730.5
Accumulated Amortization	0		$ 0		0
Trademarks and trade names
Intangible assets
Indefinite lived intangible assets useful life			Indefinite
Cost and Net	64		$ 64		64
Accumulated Amortization	0		0		$ 0
TYSABRI product | Acquired and in-licensed rights and patents
Intangible assets
Net	$ 2,633.4		$ 2,633.4

Intangible Assets and Goodwil50

Intangible Assets and Goodwill (Details 1) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Goodwill [Line Items]
Income tax benefit (expense)	$ 353.6	$ 292.5	$ 710	$ 574.4
Increase to goodwill			515
Summary of roll forward of the changes in goodwill
Goodwill, beginning of period			2,663.8
Other			(11.7)
Goodwill, end of period	$ 3,167.1		3,167.1
TECFIDERA | Fumapharm AG
Goodwill [Line Items]
Income tax benefit (expense)			85
Increase to goodwill			$ 600

Fair Value Measurements (Detail

Fair Value Measurements (Details) - USD ($) $ in Millions	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014
Assets:
Marketable debt securities	$ 5,912.4		$ 4,880.9
Fair Value, Measurements, Recurring
Assets:
Cash equivalents	874.6		909.5
Marketable equity securities	32.4		37.5
Derivative contracts	30.1		27.2
Plan assets for deferred compensation	35.6		40.1
Total	6,885.1		5,895.2
Liabilities:
Derivative contracts	24.8		14.7
Contingent consideration obligations	515.7	$ 508.3	506	$ 495.6	$ 461.8	$ 215.5
Total	540.5		520.7
Fair Value, Measurements, Recurring | Corporate debt securities
Assets:
Marketable debt securities	2,290.3		1,510.9
Fair Value, Measurements, Recurring | Government securities
Assets:
Marketable debt securities	2,973.4		2,875.9
Fair Value, Measurements, Recurring | Mortgage and other asset backed securities
Assets:
Marketable debt securities	648.7		494.1
Quoted Prices in Active Markets, Level 1 | Fair Value, Measurements, Recurring
Assets:
Cash equivalents	0		0
Marketable equity securities	32.4		37.5
Derivative contracts	0		0
Plan assets for deferred compensation	0		0
Total	32.4		37.5
Liabilities:
Derivative contracts	0		0
Contingent consideration obligations	0		0
Total	0		0
Quoted Prices in Active Markets, Level 1 | Fair Value, Measurements, Recurring | Corporate debt securities
Assets:
Marketable debt securities	0		0
Quoted Prices in Active Markets, Level 1 | Fair Value, Measurements, Recurring | Government securities
Assets:
Marketable debt securities	0		0
Quoted Prices in Active Markets, Level 1 | Fair Value, Measurements, Recurring | Mortgage and other asset backed securities
Assets:
Marketable debt securities	0		0
Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring
Assets:
Cash equivalents	874.6		909.5
Marketable equity securities	0		0
Derivative contracts	30.1		27.2
Plan assets for deferred compensation	35.6		40.1
Total	6,852.7		5,857.7
Liabilities:
Derivative contracts	24.8		14.7
Contingent consideration obligations	0		0
Total	24.8		14.7
Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring | Corporate debt securities
Assets:
Marketable debt securities	2,290.3		1,510.9
Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring | Government securities
Assets:
Marketable debt securities	2,973.4		2,875.9
Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring | Mortgage and other asset backed securities
Assets:
Marketable debt securities	648.7		494.1
Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring
Assets:
Cash equivalents	0		0
Marketable equity securities	0		0
Derivative contracts	0		0
Plan assets for deferred compensation	0		0
Total	0		0
Liabilities:
Derivative contracts	0		0
Contingent consideration obligations	515.7		506
Total	515.7		506
Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring | Corporate debt securities
Assets:
Marketable debt securities	0		0
Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring | Government securities
Assets:
Marketable debt securities	0		0
Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring | Mortgage and other asset backed securities
Assets:
Marketable debt securities	$ 0		$ 0

Fair Value Measurements (Deta52

Fair Value Measurements (Details 1) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Notes payable, carrying value	$ 6,524	$ 6,506.5
Debt instruments, fair value	7,110.9	6,645.9
Notes Payable to Fumedica
Debt Instrument [Line Items]
Notes payable, fair value	6.4	9.4
Notes payable, carrying value	6.1	9
6.875% Senior Notes due 2018
Debt Instrument [Line Items]
Notes payable, fair value	598.2	602.6
Notes payable, carrying value	561.9	565.3
2.900% Senior Notes due 2020
Debt Instrument [Line Items]
Notes payable, fair value	1,561.7	1,497.5
Notes payable, carrying value	1,507.9	1,485.5
3.625% Senior Notes due 2022
Debt Instrument [Line Items]
Notes payable, fair value	1,061	1,014.2
Notes payable, carrying value	992.7	992.2
4.050% Senior Notes due 2025
Debt Instrument [Line Items]
Notes payable, fair value	1,887.3	1,764.6
Notes payable, carrying value	1,734.1	1,733.4
5.200% Senior Notes due 2045
Debt Instrument [Line Items]
Notes payable, fair value	1,996.3	1,757.6
Notes payable, carrying value	$ 1,721.3	$ 1,721.1

Fair Value Measurements (Deta53

Fair Value Measurements (Details 2) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Business Acquisition, Contingent Consideration [Line Items]
Additions	$ 0	$ 36	$ 0	$ 274.5
Changes in fair value	10.6	(2.2)	12.9	5.6
Payments	(3.2)	0	(3.2)	0
Fair Value, Measurements, Recurring
Business Acquisition, Contingent Consideration [Line Items]
Fair value, beginning of period	508.3	461.8	506	215.5
Fair value, end of period	$ 515.7	$ 495.6	$ 515.7	$ 495.6

Fair Value Measurements (Deta54

Fair Value Measurements (Details Textual) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2016	Dec. 31, 2015
Business Acquisition, Contingent Consideration [Line Items]
Asset impairment charges	$ 0
Changes in valuation techniques	0
Contingent consideration obligations	$ 304	$ 301.3
6.875% Senior Notes due 2018
Business Acquisition, Contingent Consideration [Line Items]
Senior Notes interest rate	6.875%
2.900% Senior Notes due 2020
Business Acquisition, Contingent Consideration [Line Items]
Senior Notes interest rate	2.90%
3.625% Senior Notes due 2022
Business Acquisition, Contingent Consideration [Line Items]
Senior Notes interest rate	3.625%
4.050% Senior Notes due 2025
Business Acquisition, Contingent Consideration [Line Items]
Senior Notes interest rate	4.05%
5.200% Senior Notes due 2045
Business Acquisition, Contingent Consideration [Line Items]
Senior Notes interest rate	5.20%

Financial Instruments (Details)

Financial Instruments (Details) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015
Summary of financial assets with original maturities of less than 90 days included within cash and cash equivalents
Cash equivalents	$ 874.6	$ 909.5
Commercial paper
Summary of financial assets with original maturities of less than 90 days included within cash and cash equivalents
Cash equivalents	56.9	21.9
Overnight reverse repurchase agreements
Summary of financial assets with original maturities of less than 90 days included within cash and cash equivalents
Cash equivalents	66.3	134.7
Money market funds
Summary of financial assets with original maturities of less than 90 days included within cash and cash equivalents
Cash equivalents	531.5	673.8
Short-term debt securities
Summary of financial assets with original maturities of less than 90 days included within cash and cash equivalents
Cash equivalents	$ 219.9	$ 79.1

Financial Instruments (Details

Financial Instruments (Details 1) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015
Marketable Debt and Equity Securities
Fair Value	$ 5,912.4	$ 4,880.9
Gross Unrealized Gains	13.2	0.3
Gross Unrealized Losses	(2.1)	(10.6)
Amortized Cost	5,901.3	4,891.2
Corporate debt securities Current
Marketable Debt and Equity Securities
Fair Value	913.4	394.3
Gross Unrealized Gains	0.3	0
Gross Unrealized Losses	(0.2)	(0.5)
Amortized Cost	913.3	394.8
Corporate debt securities Non-current
Marketable Debt and Equity Securities
Fair Value	1,376.9	1,116.6
Gross Unrealized Gains	7.8	0.1
Gross Unrealized Losses	(0.4)	(4.1)
Amortized Cost	1,369.5	1,120.6
Government securities Current
Marketable Debt and Equity Securities
Fair Value	1,521.3	1,723.4
Gross Unrealized Gains	0.6	0.1
Gross Unrealized Losses	0	(1.1)
Amortized Cost	1,520.7	1,724.4
Government securities Non-current
Marketable Debt and Equity Securities
Fair Value	1,452.1	1,152.5
Gross Unrealized Gains	3.1	0
Gross Unrealized Losses	(0.6)	(3.1)
Amortized Cost	1,449.6	1,155.6
Mortgage and other asset backed securities Current
Marketable Debt and Equity Securities
Fair Value	0.1	2.8
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Amortized Cost	0.1	2.8
Mortgage and other asset backed securities Non-current
Marketable Debt and Equity Securities
Fair Value	648.6	491.3
Gross Unrealized Gains	1.4	0.1
Gross Unrealized Losses	(0.9)	(1.8)
Amortized Cost	648.1	493
Marketable equity securities
Marketable Debt and Equity Securities
Fair Value	32.4	37.5
Gross Unrealized Gains	0.9	9.2
Gross Unrealized Losses	(2.1)	0
Amortized Cost	$ 33.6	$ 28.3

Financial Instruments (Detail57

Financial Instruments (Details 2) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015
Summary of Contractual Maturities: Available-for-Sale Securities
Due in one year or less, estimated fair value	$ 2,434.8	$ 2,120.5
Due in one year or less, amortized cost	2,434.1	2,122
Due after one year through five years, Estimated Fair Value	3,255.9	2,575.9
Due after one year through five years, Amortized Cost	3,245.4	2,583.9
Due after five years, estimated fair value	221.7	184.5
Due after five years, amortized cost	221.8	185.3
Total available-for-sale securities, Fair Value	5,912.4	4,880.9
Total available-for-sale securities, Amortized Cost	$ 5,901.3	$ 4,891.2

Financial Instruments (Detail58

Financial Instruments (Details 3) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Investments, Debt and Equity Securities [Abstract]
Proceeds from maturities and sales	$ 1,642.5	$ 601.9	$ 2,823.6	$ 975.5
Realized gains	0.6	0.3	1	0.5
Realized losses	$ (1.2)	$ (0.5)	$ (1.6)	$ (0.8)

Financial Instruments (Detail59

Financial Instruments (Details Textual)	6 Months Ended	12 Months Ended
	Jun. 30, 2016	Dec. 31, 2015
Investments, Debt and Equity Securities [Abstract]
Overnight reverse repurchase agreements, percent of total assets	0.30%	0.70%
Average maturity of marketable securities, months	13 months	16 months

Financial Instruments Financial

Financial Instruments Financial Instruments (Details Textual 2) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015
Strategic Investments
Business Acquisition [Line Items]
Strategic investment portfolio	$ 98.3	$ 96

Derivative Instruments (Details

Derivative Instruments (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Derivative Instruments (Textual) [Abstract]
Gain/Loss on fair value of foreign currency forward contracts	$ 16.4		$ 16.4		$ 1.8
Expected settlement time for contracts, in months			18 months
Net gains (losses) of other income (expense) related to foreign currency forward contracts	18.6	$ 13.6	$ 16.2	$ 3.9
Minimum
Derivative Instruments (Textual) [Abstract]
Range of durations of foreign currency forward contracts			1 month		1 month
Maximum
Derivative Instruments (Textual) [Abstract]
Range of durations of foreign currency forward contracts			18 months		18 months
Not designated as hedging instrument
Derivative Instruments (Textual) [Abstract]
Aggregate notional amount	557.2		$ 557.2		$ 721
Other current assets | Designated as hedging instrument
Summary of Derivatives designated as Hedging Instruments
Derivative asset, fair value, net	2		2		16.6
Investments and other assets | Designated as hedging instrument
Summary of Derivatives designated as Hedging Instruments
Derivative asset, fair value, net	23.6		23.6		0.3
Accrued expenses and other | Designated as hedging instrument
Summary of Derivatives designated as Hedging Instruments
Derivative liability, fair value, net	14.8		14.8		10.2
Other long-term liabilities | Designated as hedging instrument
Summary of Derivatives designated as Hedging Instruments
Derivative liability, fair value, net	0		0		2.5
Foreign exchange contract | Designated as hedging instrument
Derivative Instruments (Textual) [Abstract]
Aggregate notional amount	1,209.9		1,209.9		1,103
Foreign exchange contract | Other current assets | Not designated as hedging instrument
Summary of Derivatives designated as Hedging Instruments
Derivative asset, fair value, net	4.5		4.5		10.3
Foreign exchange contract | Accrued expenses and other | Not designated as hedging instrument
Summary of Derivatives designated as Hedging Instruments
Derivative liability, fair value, net	10		10		2
Interest rate swap | Designated as hedging instrument
Derivative Instruments (Textual) [Abstract]
Aggregate notional amount	675		675
Revenue | Foreign exchange contract
Derivative Instruments (Textual) [Abstract]
Net gains (losses) in product revenue for the settlement of certain effective cash flow hedge instruments	(4.3)	40.4	4.5	75.4
Operating expense | Foreign exchange contract
Derivative Instruments (Textual) [Abstract]
Net gains (losses) in product revenue for the settlement of certain effective cash flow hedge instruments	(0.1)	0	(0.2)	0
Other income (expense) | Cash flows, revenue | Foreign exchange contract
Derivative Instruments (Textual) [Abstract]
Net gains (losses) in earnings of Foreign currency forward contracts due to hedge ineffectiveness	2.1	1.2	4	3.4
Other income (expense) | Cash flows, operating expenses | Foreign exchange contract
Derivative Instruments (Textual) [Abstract]
Net gains (losses) in earnings of Foreign currency forward contracts due to hedge ineffectiveness	0	$ 0	(0.3)	$ 0
Euro | Foreign exchange contract | Designated as hedging instrument
Derivative Instruments (Textual) [Abstract]
Aggregate notional amount	1,126.5		1,126.5		945.5
Swiss francs | Foreign exchange contract | Designated as hedging instrument
Derivative Instruments (Textual) [Abstract]
Aggregate notional amount	43.5		43.5		80.8
Canadian Dollar | Foreign exchange contract | Designated as hedging instrument
Derivative Instruments (Textual) [Abstract]
Aggregate notional amount	$ 39.9		$ 39.9		$ 76.7
2.900% Senior Notes due 2020
Derivative Instruments (Textual) [Abstract]
Senior Notes interest rate	2.90%		2.90%

Property, Plant and Equipment62

Property, Plant and Equipment Property, Plant and Equipment (Details) SFr in Millions, $ in Millions	3 Months Ended
	Jun. 30, 2016USD ($)	Dec. 31, 2015CHF (SFr)	Dec. 31, 2015USD ($)
Property, Plant and Equipment [Line Items]
Accumulated depreciation	$ 1,471		$ 1,330.1
Property, plant and equipment, net	2,301.8		2,187.6
Solothurn, Switzerland
Property, Plant and Equipment [Line Items]
Construction in progress	247.8		99
Solothurn, Switzerland | Land
Property, Plant and Equipment [Line Items]
Land purchase		SFr 64.4	$ 62.5
Cambridge, MA
Property, Plant and Equipment [Line Items]
Property, plant and equipment, net	43
Remaining lease obligation	26.3
Accelerated depreciation	$ 15.8

Equity (Details)

Equity (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Reconciliation of equity attributable to non-controlling interests
NCI, beginning of period	$ 1.3	$ 2.7	$ 2.1	$ 5
Net income (loss) attributable to NCI, net of tax	(1.4)	(2.5)	(3.1)	(4.8)
Fair value of net assets and liabilities acquired and assigned to NCI	0	0	0.9	0
Translation adjustment and other	0	(0.2)	0	(0.2)
NCI, end of period	$ (0.1)	$ 0.4	$ (0.1)	$ 0.4

Equity (Details Textual)

Equity (Details Textual) - USD ($) shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Jul. 18, 2016	May 31, 2015
Subsequent Event [Line Items]
Authorized amount of share repurchases under the 2015 Share Repurchase Program						$ 5,000
Equity increase during the period			$ 2,028.8
Net income attributable to Biogen Inc.	$ 1,049.8	$ 927.3	$ 2,020.7	$ 1,749.8
Common stock shares authorized for repurchased	1.3		1.3
Repurchase of common stock, shares				0.1
Purchase of treasury stock			$ 0	$ 42.2
Subsequent event
Subsequent Event [Line Items]
Authorized amount of share repurchases under the 2015 Share Repurchase Program					$ 5,000

Accumulated Other Comprehensi65

Accumulated Other Comprehensive Income (Loss) Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Accumulated other comprehensive income [Line Items]
Balance, as of the beginning of the period			$ (224)	$ (59.5)
Other comprehensive income loss before reclassifications			(54.8)	33.3
Amounts reclassified from accumulated other comprehensive income loss			(4)	(74.8)
Net current period other comprehensive income loss	$ (23.5)	$ (30.5)	(58.8)	(41.5)
Balance, as of the end of the period	(282.8)	(101)	(282.8)	(101)
Accumulated Net Unrealized Investment Gain (Loss)
Accumulated other comprehensive income [Line Items]
Balance, as of the beginning of the period			(0.8)	(0.4)
Other comprehensive income loss before reclassifications			6.6	0.9
Amounts reclassified from accumulated other comprehensive income loss			0.4	0.2
Net current period other comprehensive income loss			7	1.1
Balance, as of the end of the period	6.2	0.7	6.2	0.7
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges
Accumulated other comprehensive income [Line Items]
Balance, as of the beginning of the period			10.2	71.7
Other comprehensive income loss before reclassifications			(13.9)	66.1
Amounts reclassified from accumulated other comprehensive income loss			(4.4)	(75)
Net current period other comprehensive income loss			(18.3)	(8.9)
Balance, as of the end of the period	(8.1)	62.8	(8.1)	62.8
Accumulated Defined Benefit Plans Adjustment
Accumulated other comprehensive income [Line Items]
Balance, as of the beginning of the period			(37.8)	(31.6)
Other comprehensive income loss before reclassifications			0.9	4.1
Amounts reclassified from accumulated other comprehensive income loss			0	0
Net current period other comprehensive income loss			0.9	4.1
Balance, as of the end of the period	(36.9)	(27.5)	(36.9)	(27.5)
Accumulated Translation Adjustment
Accumulated other comprehensive income [Line Items]
Balance, as of the beginning of the period			(195.6)	(99.2)
Other comprehensive income loss before reclassifications			(48.4)	(37.8)
Amounts reclassified from accumulated other comprehensive income loss			0	0
Net current period other comprehensive income loss			(48.4)	(37.8)
Balance, as of the end of the period	$ (244)	$ (137)	$ (244)	$ (137)

Accumulated Other Comprehensi66

Accumulated Other Comprehensive Income (Loss) Accumulated Other Comprehensive Income (Loss) (Details 1) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other income (expense), net	$ (58.5)	$ (10.9)	$ (111.3)	$ (25.9)
Income tax benefit (expense)	353.6	292.5	710	574.4
Product, net	(2,466)	(2,198.6)	(4,775.4)	(4,370.9)
Net income attributable to Biogen Inc.	1,049.8	927.3	2,020.7	1,749.8
Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net income attributable to Biogen Inc.	(4.7)	40.1	4	74.8
Accumulated Net Unrealized Investment Gain (Loss) | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other income (expense), net	(0.6)	(0.2)	(0.6)	(0.3)
Income tax benefit (expense)	0.2	0.1	0.2	0.1
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other income (expense), net	0	0	0.1	0
Income tax benefit (expense)	0.1	(0.2)	0	(0.4)
Product, net	(4.3)	(40.4)	(4.5)	(75.4)
Operating expenses	$ (0.1)	$ 0	$ (0.2)	$ 0

Earnings per Share (Details)

Earnings per Share (Details) - USD ($) shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Numerator:
Net income attributable to Biogen Inc	$ 1,049.8	$ 927.3	$ 2,020.7	$ 1,749.8
Weighted-average shares used in calculating:
Weighted average number of common shares outstanding	219.1	235.3	219	235.1
Effect of dilutive securities:
Dilutive potential common shares	0.3	0.4	0.3	0.6
Shares used in calculating diluted earnings per share	219.4	235.7	219.3	235.7
Stock options and employee stock purchase plan
Effect of dilutive securities:
Stock units	0.1	0.1	0.1	0.1
Time-vested restricted stock units
Effect of dilutive securities:
Stock units	0.1	0.2	0.1	0.3
Market stock units
Effect of dilutive securities:
Stock units	0.1	0.1	0.1	0.2

Share-Based Payments (Details)

Share-Based Payments (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Share-based Compensation Expense included in consolidated statements of income
Subtotal	$ 50.2	$ 48.3	$ 104.5	$ 139.3
Capitalized share-based compensation costs	(4.4)	(2.2)	(7.5)	(5.6)
Share-based compensation expense included in total costs and expenses	45.8	46.1	97	133.7
Income tax effect	(12.7)	(12.9)	(27.9)	(39.6)
Research and development
Share-based Compensation Expense included in consolidated statements of income
Share-based compensation expense	(21.5)	(22.1)	(42.9)	(57.5)
Selling, general and administrative
Share-based Compensation Expense included in consolidated statements of income
Share-based compensation expense	(28.7)	(26.2)	(63.4)	(81.8)
Restructuring charges
Share-based Compensation Expense included in consolidated statements of income
Share-based compensation expense	0	0	(1.8)	0
Total share-based compensation expense, net of tax
Share-based Compensation Expense included in consolidated statements of income
Share-based compensation expense	$ (33.1)	$ (33.2)	$ (69.1)	$ (94.1)

Share-Based Payments (Details 1

Share-Based Payments (Details 1) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Summary of share based compensation expense associated with different programs
Subtotal	$ 50.2	$ 48.3	$ 104.5	$ 139.3
Capitalized share-based compensation costs	(4.4)	(2.2)	(7.5)	(5.6)
Share-based compensation expense included in total costs and expenses	45.8	46.1	97	133.7
Market stock units
Summary of share based compensation expense associated with different programs
Share-based compensation expense	7.9	9.1	21.3	26.1
Time-vested restricted stock units
Summary of share based compensation expense associated with different programs
Share-based compensation expense	33.9	31.8	64	63.7
Cash settled performance shares
Summary of share based compensation expense associated with different programs
Share-based compensation expense	4.6	3.2	4.8	27
Performance units
Summary of share based compensation expense associated with different programs
Share-based compensation expense	1.3	1.2	8.2	14.4
Employee stock purchase plan
Summary of share based compensation expense associated with different programs
Share-based compensation expense	$ 2.5	$ 3	$ 6.2	$ 8.1

Share-Based Payments (Details 2

Share-Based Payments (Details 2) - shares	6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015
Market stock units
Schedule of stock option grants
Stock units	166,000	179,000
Cash settled performance shares
Schedule of stock option grants
Stock units	86,000	115,000
Performance units
Schedule of stock option grants
Stock units	56,000	89,000
Time-vested restricted stock units
Schedule of stock option grants
Stock units	594,000	375,000

Share-Based Payments (Details T

Share-Based Payments (Details Textual) - shares	6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015
Employee Stock Ownership Plan (ESOP) Disclosures [Line Items]
Employee stock purchase plan maximum shares		6,200,000
1995 ESPP
Employee Stock Ownership Plan (ESOP) Disclosures [Line Items]
Shares issued under ESPP		98,000
2015 ESPP
Employee Stock Ownership Plan (ESOP) Disclosures [Line Items]
Shares issued under ESPP	109,000

Income Taxes (Details)

Income Taxes (Details)	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Reconciliation between the U.S. federal statutory tax rate and effective tax rate
Statutory rate	35.00%	35.00%	35.00%	35.00%
State taxes	1.00%	0.40%	1.00%	0.00%
Taxes on foreign earnings	(10.00%)	(11.10%)	(9.00%)	(9.80%)
Credits and net operating loss utilization	(1.20%)	(0.70%)	(1.20%)	(0.70%)
Purchased intangible assets	1.10%	1.10%	1.10%	1.00%
Manufacturing deduction	(1.60%)	(2.10%)	(1.70%)	(1.80%)
Permanent items	0.60%	0.90%	0.60%	0.70%
Other	0.30%	0.40%	0.20%	0.30%
Effective tax rate	25.20%	23.90%	26.00%	24.70%

Income Taxes (Details Textual)

Income Taxes (Details Textual) - USD ($) $ in Millions	1 Months Ended	6 Months Ended
	Oct. 31, 2011	Jun. 30, 2016	Jun. 30, 2015
Income Tax Contingency [Line Items]
Net benefit for a previously unrecognized position			$ 24
Tax Year 2007
Income Tax Contingency [Line Items]
Proposed deduction disallowance by tax authorities	$ 130
Tax Year 2008
Income Tax Contingency [Line Items]
Proposed deduction disallowance by tax authorities	130
Tax Year 2009
Income Tax Contingency [Line Items]
Proposed deduction disallowance by tax authorities	$ 130
SKAT
Income Tax Contingency [Line Items]
Notice of assessment of corporate withholding tax including penalties and interest		$ 66.9
Payments to taxing authority		$ 13

Other Consolidated Financial 74

Other Consolidated Financial Statement Detail (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Accrued Expenses and Other
Revenue-related reserves for discounts and allowances	$ 651.8		$ 651.8		$ 662.7
Current portion of contingent consideration obligations and milestones	556.7		556.7		504.7
Employee compensation and benefits	228.4		228.4		270.8
Royalties and licensing fees	183.7		183.7		167.9
Other	613.4		613.4		635.3
Total accrued expenses and other	2,072.7		2,072.7		2,096.8
Other Income (Expense), Net
Interest income	15.4	$ 4.3	26.6	$ 7.6
Interest expense	(65.9)	(5.8)	(129.2)	(12.5)
Gain (loss) on sales of investments, net	(2.7)	0.3	(1.1)	(1.4)
Foreign exchange gains (losses), net	0.2	(1.5)	2.3	(14.5)
Other, net	(5.5)	(8.2)	(9.9)	(5.1)
Other income (expense), net	(58.5)	$ (10.9)	(111.3)	$ (25.9)
Component of accrued expenses and other
Accrued Expenses and Other
Revenue-related reserves for discounts and allowances	$ 490.5		$ 490.5		$ 518.1

Other Consolidated Financial 75

Other Consolidated Financial Statement Detail Other Consolidated Financial Statement (Details Textual) € in Millions, $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2016USD ($)	Jun. 30, 2015USD ($)	Jun. 30, 2014USD ($)	Jun. 30, 2016USD ($)	Jun. 30, 2015USD ($)	Jun. 30, 2016EUR (€)	Dec. 31, 2015USD ($)
Product Liability Contingency [Line Items]
Prepaid taxes	$ 704.1			$ 704.1			$ 550.6
Product, net	$ 2,466	$ 2,198.6		$ 4,775.4	$ 4,370.9
Italy
Product Liability Contingency [Line Items]
Reimbursement limit stated in the resolution			24 months
Product, net			$ 53.5
Amount reserved for this matter | €						€ 75

Investments in Variable Inter76

Investments in Variable Interest Entities (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2016	Dec. 31, 2015
Variable Interest Entity [Line Items]
Investment in biotechnology companies that are determined to be unconsolidated variable interest entities	$ 38	$ 29.2
Neurimmune
Variable Interest Entity [Line Items]
Remaining potential development milestone payments and royalties on commercial sales under the terms of collaboration agreement	$ 275
Research and development cost in support of collaboration agreement	100.00%
Other Variable Interest Entities
Variable Interest Entity [Line Items]
Additional investments committed to if certain development milestones are achieved	$ 8

Collaborative and Other Relat77

Collaborative and Other Relationships Collaborative and Other Relationships - Collaborations (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015	Jan. 31, 2007
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Research and development	$ 473.1	$ 490.7	$ 910.4	$ 951.3
Investments and other assets	1,153		$ 1,153		$ 1,107.6
Sobi rate to Biogen on net sales in the Sobi Territory
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Reimbursement under the amended agreement method			Royalty
Base rate after first commercial sale			12.00%
Rate during the reimbursement period			Base Rate plus 5%
Biogen rate to Sobi on net sales in the Biogen North America Territory
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Reimbursement under the amended agreement method			Royalty
Rate during the reimbursement period			Base Rate less 5%
Biogen rate to Sobi on net sales in the Biogen North America Territory | Sobi Territory
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Base rate after first commercial sale			12.00%
Biogen rate to Sobi on net sales in the Biogen Direct Territory
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Reimbursement under the amended agreement method			Royalty
Rate during the reimbursement period			Base Rate less 5%
Biogen rate to Sobi on net sales in the Biogen Direct Territory | Sobi Territory
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Base rate after first commercial sale			17.00%
Biogen rate to Sobi on net revenue from the Biogen Distributor Territory
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Reimbursement under the amended agreement method			Net Revenue Share
Rate during the reimbursement period			Base Rate less 15%
Biogen rate to Sobi on net revenue from the Biogen Distributor Territory | Sobi Territory
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Base rate after first commercial sale			50.00%
Biogen Hemophilia
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Percentage of stock acquired						100.00%
University of Pennsylvania
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Research and development	20
Investments and other assets	15		$ 15
Future research and development commitment	47.5		47.5
Potential future milestone payments	$ 2,000		$ 2,000
Swedish Orphan Biovitrum
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Reimbursement recognition period			10 years
Reimbursement cost achieving period			6 years
Time period for paying remaining balance due			90 days
Swedish Orphan Biovitrum | ELOCTATE
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Research and development			$ 157
Swedish Orphan Biovitrum | ALPROLIX
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Research and development			$ 130

Collaborative and Other Relat78

Collaborative and Other Relationships Collaborative and Other Relationships - Equity Method Investments (Details) $ in Millions, ₩ in Billions	1 Months Ended	3 Months Ended			6 Months Ended
	Feb. 29, 2012USD ($)	Jun. 30, 2016USD ($)	Jun. 30, 2015USD ($)	Dec. 31, 2013USD ($)	Jun. 30, 2016USD ($)	Jun. 30, 2015USD ($)	Feb. 29, 2012KRW (₩)
Schedule of Equity Method Investments [Line Items]
Recognized loss		$ 0	$ (4.9)		$ 0	$ (5.7)
Research and development		473.1	490.7		910.4	951.3
Revenue related to technical development and technology transfer services		$ 79	55.6		$ 166.9	107.6
Samsung Biosimilar Agreement [Member]
Schedule of Equity Method Investments [Line Items]
Contribution from Samsung to develop, manufacture and market biosimilar pharmaceuticals	$ 250						₩ 280.5
Variable interest entity, qualitative or quantitative information, ownership percentage	85.00%
Contribution from Biogen to develop, manufacture and market biosimilar pharmaceuticals	$ 45						₩ 49.5
Percentage of stake in entity minimum	15.00%	9.00%			9.00%		15.00%
Percentage of stake in entity maximum	49.90%
Recognized loss			(4.9)			(5.7)
Research and development				$ 46
Expected profit share with Samsung Bioepis				50.00%
Revenue related to technical development and technology transfer services		$ 14.2	$ 17.2		$ 16.9	$ 36.1
Acquired and in-licensed rights and patents | Biosimilars
Schedule of Equity Method Investments [Line Items]
Increase in acquired and in-licensed rights and patents		$ 25			$ 50

Litigation (Details)

Litigation (Details)	3 Months Ended
	Jun. 30, 2014
Italy
Loss Contingencies [Line Items]
Reimbursement limit stated in the resolution	24 months

Commitments and Contingences (D

Commitments and Contingences (Details) - Fumapharm AG - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2016	Dec. 31, 2006	Jun. 30, 2013
Business Acquisition, Contingent Consideration [Line Items]
Cash portion of consideration	$ 600	$ 220
TECFIDERA
Business Acquisition, Contingent Consideration [Line Items]
Maximum contingent consideration in the form of development and approval milestones			$ 15
Seven billion
Business Acquisition, Contingent Consideration [Line Items]
Cumulative sales level	7,000
Eight billion
Business Acquisition, Contingent Consideration [Line Items]
Cumulative sales level	8,000
Nine billion
Business Acquisition, Contingent Consideration [Line Items]
Cash portion of consideration	300
Cumulative sales level	9,000
Each additional one billion up to twenty billion
Business Acquisition, Contingent Consideration [Line Items]
Cumulative sales level	20,000
One billion
Business Acquisition, Contingent Consideration [Line Items]
Cumulative sales level	1,000
Three billion
Business Acquisition, Contingent Consideration [Line Items]
Cumulative sales level	$ 3,000

Commitments and Contingencies C

Commitments and Contingencies Commitments and Contingencies (Details 1) $ in Millions	Jun. 30, 2016USD ($)
Switzerland
Long-term Purchase Commitment [Line Items]
Contractual commitments for the construction of the facility	$ 226